Antigen-independent adhesion of CD4 CD45RA T cells from cord blood

Antigen-independent adhesion of resting adult CD4⁺ CD45RO⁺ T cells to B lymphocytes has been shown to be transient and can be down-regulated by CD4 major histocompatibility complex (MHC) class II molecule interactions. Conversely, adhesion of adult CD4+ CD45RA+ subpopulation to B cells is not regulated by ligands of CD4. We have investigated the regulation of adhesion of cord blood CD45RA⁺ CD4⁺ T lymphocytes. In contrast to adult CD45RA⁺ CD4⁺ T cells, cord blood CD45RA⁺ CD4⁺ T cells were strongly sensitive to the down-regulation of adhesion mediated by the CD4-HLA class II interaction, since adhesion to MHC class II(⁺) B cells was transient and inhibited by an anti-CD4 antibody. In addition, human immunodeficiency virus gpl60, synthetic gpl06-derived peptides encompassing a CD4 binding site inhibited conjugate formation between cord blood CD45RA⁺ CD4+ T cells and B cells. Following activation of the cord blood CD4 T cells by an anti-CD3 antibody, a conversion from a transient to a stable adhesion pattern of cord blood CD4 T cells to B cells occurred in 2 days. The reversal to a transient adhesion occurred at day 8 following anti-CD3 activation in correlation with a complete shift to a CD45RO phenotype of the cord blood CD4 T cells. These data suggest that CD4 T cell adhesion can be developmentally regulated.     

Antigen-independent responsiveness to interleukin-4 demonstrates differential regulation of newborn human T cells

The low incidence of graft-versus-host disease following clinical use of umbilical cord blood compared to adult bone marrow as a source of stem cells for bone marrow reconstitution, leads to questions concerning the level of immunocom-petence of newborn T cells. The maturation and functional status of newborn CD4⁺ T cells, which are almost exclusively CD45RA⁺ naive T cells, compared with their adult phenotypic counterparts, is poorly understood. We examined the proliferative response to mitogens and cytokines of CD4/CD45RA⁺ T cells from adults and newborns, with and without accessory cells. Newborn CD4/CD45RA⁺ T cells demonstrated a distinct proliferative response profile which was determined by the number of accessory cells present in co-cultures with various stimuli. Newborn CD4/CD45RA⁺ T cells were particularly responsive to interleukin (IL)-4, IL-4 plus anti-CD2 monoclonal antibodies (mAb) and IL-4 plus phytohemagglutinin (PHA), whereas adult CD4/CD45RA⁺ T cells were unresponsive under similar conditions. The mitogenic responses of newborn and adult CD4/CD45RA⁺ T cells to PHA and anti-CD2 mAb, which were equivalent, were directly proportional to the number of accessory cells present, whereas the responsiveness to cytokines was inversely proportional to the number of co-cultured accessory cells. Anti-CD2 responses were much more sensitive to low numbers of accessory cells than PHA. The particular sensitivity of newborn CD4/CD45RA⁺ T cells to IL-4 represents an antigen-independent T cell activation response which could help promote a Th2 immune response resulting in the newborn.     

CD45RB expression defines two interconvertible subsets of human CD4+ T cells with memory function

Reciprocal expression of CD45RA and CD45RO in human CD4⁺ T cells defines populations understood to be naive cells (CD45RA⁺CD45RO^?) and memory cells (CD45RA^?CD45RO⁺). We investigate two subsets of CD45RA^?CD45RO⁺ CD4⁺ human T cells which differ by fourfold in their expression of the CD45RB isoform; one is CD45RB^bright and the other is CD45RB^intermediate. In contrast, CD45RA⁺ naive cells are all CD45RB^bright. Both subsets of CD45RA^? cells proliferate in response to recall antigens so we designate them MEM 1 (CD45RO⁺RB^bright) and MEM 2 (CD45RO⁺RB^intermediate). CD45RA and CD45RB expression are regulated independently during in vitro activation of naive cells. When MEM 1 cells are activated they tend to down-regulate CD45RB expression, whereas activated MEM 2 cells tend to up-regulate CD45RB expression. Thus, in contrast to the stability of the CD45RA^?CD45RO⁺ phenotype, the MEM 1 and MEM 2 phenotypes are labile and may interconvert. MEM 1 and MEM 2 cells produced comparable amounts of interleukin(IL)?2, IL?4, and IL-5 though MEM 1 cells produced slightly more interferon(IFN)-γ (mean 1.7-fold more). MEM 1 cells consistently proliferated more (mean 2.3-fold more) than MEM 2 cells early during in vitro activation. Thus, differential expression of CD45RB within CD45RA^? cells defines two subsets that have similar properties except for somewhast greater IFN-γ production and proliferative responses by MEM 1 cells. Variability in CD45RB expression may represent a mechanism for fine-tuning the responsiveness of memory cells in vivo.     

Age-related accumulation of LFA-1high cells in a CD8+CD45RAhigh T cell population

The differential expression of CD45 isoforms has been suggested as a marker for stages of post-thymic T cell development, that is, CD45RA+CD45R0^? T cells and CD45RA^?CD45R0⁺ T cells are supposed to be virgin and memory cells respectively. Recently, several adhesion molecules have been shown to be up-regulated on the cell surface of memory T cells, and have been suggested to serve as a memory marker. In this study, we investigated the levels of LFA-1 expression on T cells in various subpopulations defined by CD45 isoform expression in donors of various ages. In CD4⁺ T cells, the proportion of LFA-1^high cells among CD45RA^highCD45R0-T cells remained low in all age groups and did not show significant accumulation with age. CD4⁺CD45RA^?CD45R0^highTcells expressed LFA-1 at a higher level than CD4⁺CD45RA^highCD45R0^? T cells. Thus, the currently prevailing view that CD45RA and CD45R0 can be markers for virgin and primed cells was consistent with LFA-1 expression in CD4⁺ T cell population. In CD8⁺ T cells, however, CD45RA^highCD45R0^? T cells consisted of two distinct subpopulations, LFA-1^low and LFA-1^high cells, whereas CD45RA^?CD45R0^high T cells were almost exclusively LFA-1^high When CD29 expression was examined in place of LFA-1 expression, similar results were obtained; CD45RA^high CD45R0^? T cells consisted of two distinct subpopulations, CD29-^{to low} and CD^29high cells, while CD45RA-CD45R0^high T cells were mostly CD29^high. The proportion of LFA-1^high cells in the CD8+CD45RA^high T cell subpopulation increased significantly as a function of age (r = 0.9, p < 0.001). It ranged from 8% in a 14-year-old donor to 94% in a 79-year-old donor. Furthermore, the proportion of CD8⁺CD45RA^highLFA-1^high cells in the CD8⁺ T cell population increased significantly as a function of age (r = 0.85, p < 0.001). On the other hand, the proportion of LEA-1^high cells in CD8⁺CD45RA^? T cell subpopulation exceeded 90% in most donors irrespective of age. These results indicate that the CD8⁺CD45RA^highCD45R0^? T cell subpopulation contains a considerable number of LFA-1^high cells and CD29^high cells, phenotypically similar to previously activated cells. Thus, in terms of LFA-1 and CD29 expressions, the simple scheme that CD45RA is a marker of virgin cells is not applicable to the CD8⁺ T cell population.     

Interleukin-13 is produced by activated human CD45RA+ and CD45R0+ T cells: modulation by interleukin-4 and interleukin-12

Interleukin (IL)-13 is a cytokine originally identified as a product of activated T cells. Little is known, however, about IL-13 production by human T cells and its modulation by other cytokines. Here, we show that IL-13 is produced by activated human CD4⁺ and CD8⁺ CD45R0⁺ memory T cells and CD4⁺ and CD8⁺ CD45RA⁺ naive T cells. In contrast, IL-4, which shares many biological activities with IL-13, is only produced by CD45R0⁺ T cells following activation. Analysis of intracellular cytokine production by single CD45RA⁺ and CD45R0⁺ T cells indicated that IL-13 continued to be produced for more than 24 h after stimulation, whereas IL-4 could not be detected after 24 h. These data were confirmed by measurement of specific mRNA and suggest that IL-13, unlike IL-4, but like interferon-γ (IFN-γ), is a cytokine with long-lasting kinetics. The majority of human CD45R0⁺ T cells produced IL-4 and IL-13 simultaneously. In contrast, IFN-γ protein was generally not co-expressed with IL-4 or IL-13. IL-4 added to primary cultures of highly purified peripheral blood T cells activated by the combination of anti-CD3+anti-CD28 mAb enhanced IL-13 production by CD45RA⁺ and to a lesser extent by CD45R0⁺ T cells. Under these conditions, however, IL-12 inhibited IL-13 production by CD45RA⁺ T cells and to a lesser extent by CD45R0⁺ T cells in a dose-dependent fashion. These inhibiting effects were not related to enhanced IFN-γ production induced by IL-12, since IFN-γ by itself did not affect IL-13 production. Collectively, our data indicate that IL-13 is produced by peripheral blood T cells which also produce IL-4, but not IFN-γ, and by naive CD45RA⁺ T cells which, in contrast, fail to produce IL-4. These observations, together with the long-lasting production of IL-13, suggest that IL-13 may have IL-4-like functions in situations where T cell-derived IL-4 is still absent or where its production has already been down-regulated.     

In vitro responses of human CD45R0brightRA− and CD45R0−RAbright T cell subsets and their relationship to memory and naive T cells

The cellular basis of immunological memory, particularly with respect to T cells is not understood. In humans, monoclonal antibodies to CD45 have been used to identify memory (CD45R0) and naive (CD45RA) T cells. However, this identification has been called into question by various studies which suggest that high molecular weight CD45 isoforms may be re-expressed by previously activated cells. In the present study, using cultures which supported responses of naive T cells, we examined the responses of purified CD45R0^brightRA^? or CD45R0^?-RA^bright T cell subsets. The former subset was found to respond preferentially to recall antigens with minimal responses apparent to neo-(or non-recall)-antigens. The inverse pattern was found for CD45R0^?RA^bright T cells, which converted to CD45R0^brightRA^? after stimulation with a neo-antigen. Moreover, the two populations of T cells exhibited distinct response kinetics with a faster response evident from the CD45R0^brightRA^?T cells compared to the CD45R0^?RA^bright subset. The poor responses of CD45R0^?RA^bright T cells to recall antigens compared to neo-antigens suggests that this putative naive population is specifically depleted of reactive T cells following an encounter with antigen. We propose that T cell priming results in the stimulation of many CD45R0^?RA^bright T cells with various T cell receptor specificities from which memory T cells are selected for survival. If re-expression of higher molecular weight isoforms does occur in humans in vivo, our results suggest that R0 expression would be retained (CD45R0⁺RA⁺). Alternatively, if primed CD45R0^?RA^bright T cells exist, they are not prevalent in peripheral blood and thus may be sequestered within lymphoid tissues. Our data support the view that in human peripheral blood, CD45R0^bright and CD45RA^bright expression identify memory and naive CD4⁺ T cells, respectively.     

The CD7− T cell subset represents the majority of IL-5-secreting cells within CD4+CD45RA− T cells

Absence of CD7 is a stable phenotype in a subset of normal human T cells. Most circulating CD7⁻ T cells express the CD4⁺CD45RO⁺CD45RA⁻ memory phenotype. We analysed CD4⁺CD45RA⁻ peripheral blood lymphocytes that were separated into CD7⁺ and CD7⁻ for their in vitro cytokine secretion in response to different stimuli. The CD4⁺CD7⁻ subpopulation was found to secrete significantly higher levels of IL-5 compared with the CD4⁺CD7⁺ subset upon stimulation with ionomycin/phorbol myristate acetate (PMA) plus anti-CD28 MoAbs. In contrast to IL-5 secretion, IL-4 and interferon-gamma (IFN-γ) secretion was not significantly different in CD7⁺ and CD7⁻ T cells upon stimulation in vitro. The data indicate that the CD4⁺CD7⁻ T cell represents the majority of IL-5-secreting cells within the population of CD4⁺CD45RA⁻ memory T cells. Since CD4⁺CD7⁻ T cells were found to be enriched in various skin lesions associated with eosinophilic infiltration, the results of our study support the hypothesis that skin-infiltrating CD7⁻ T cells are one of the major sources of IL-5 responsible for the development of eosinophilic inflammation in certain skin diseases.     

CCR7+ Central and CCR7− Effector Memory CD4+ T Cells in Human Cutaneous Leishmaniasis

Purpose

The profile of central (=T_CM) and effector (=T_EM) memory CD4⁺ T cell subsets and the possible role as surrogate markers of protection is studied in the volunteers with history of cutaneous leishmaniasis (HCL).

Methods

Profile of T cell subsets based on CCR7/CD45RA expressions and phenotypic changes after soluble Leishmania antigen (SLA) stimulation were analyzed. Then, sorted CD4⁺CD45RO^?CD45RA⁺ naïve T, CD4⁺CD45RO⁺CD45RA^?CCR7^? T_EM, CD4⁺CD45RO⁺CD45RA^?CCR7⁺ T_CM subsets were cultured with SLA for proliferation, cytokine production and intracellular cytokine assays.

Results

In the HCL and control volunteers, the mean frequencies of CD4⁺CD45RA⁺CCR7⁺ naïve T cells and CD4⁺CD45RA^?CCR7^? T_EM cells were higher than the other subsets before culture. Frequency of naïve T cells and CD4⁺CD45RA^?CCR7⁺ T_CM cells was significantly decreased (P?=?0.01 for naïve T and P?<?0.05 for T_CM cells) and frequency of T_EM cells was significantly increased after SLA stimulation compared to before culture (P?<?0.001). By CFSE labeling, CD4⁺CD45RO⁺CD45RA^?CCR7⁺ T_CM cells showed more proliferation potential than CD4⁺CD45RO⁺CD45RA^?CCR7^? T_EM cells. Stimulation of the T_EM cells in HCL volunteers induced a significantly higher IFN-γ production (P?=?0.04) with higher number of intracellular IFN-γ positive cells (P?=?0.032) than the same cells from controls. A significantly higher number of T_CM cells produced IL-2 in HCL volunteers compared with controls (P?<?0.05). Most of the intracellular IFN-γ positive T_EM cells were proliferating CFSE-dim populations (P?<?0.05).

Conclusions

A combination of Leishmania-reactive IFN-γ producing CD4⁺CD45RO⁺CD45RA^?CCR7^? T_EM and Leishmania-reactive IL-2 producing CD4⁺CD45RO⁺CD45RA^?CCR7⁺ T_CM are identified in individuals with history of CL which might play a role in protective recall immune response against Leishmania infection.     

Cytomegalovirus infection induces the accumulation of short-lived, multifunctional CD4+CD45RA+CD27+ T cells: the potential involvement of interleukin-7 in this process

The relative roles that ageing and lifelong cytomegalovirus (CMV) infection have in shaping naive and memory CD4⁺ T-cell repertoires in healthy older people is unclear. Using multiple linear regression analysis we found that age itself is a stronger predictor than CMV seropositivity for the decrease in CD45RA⁺ CD27⁺ CD4⁺ T cells over time. In contrast, the increase in CD45RA⁻ CD27⁻ and CD45RA⁺ CD27⁻ CD4⁺ T cells is almost exclusively the result of CMV seropositivity, with age alone having no significant effect. Furthermore, the majority of the CD45RA⁻ CD27⁻ and CD45RA⁺ CD27⁻ CD4⁺ T cells in CMV-seropositive donors are specific for this virus. CD45RA⁺ CD27⁻ CD4⁺ T cells have significantly reduced CD28, interleukin-7 receptor α (IL-7Rα) and Bcl-2 expression, Akt (ser473) phosphorylation and reduced ability to survive after T-cell receptor activation compared with the other T-cell subsets in the same donors. Despite this, the CD45RA⁺ CD27⁻ subset is as multifunctional as the CD45RA⁻ CD27⁺ and CD45RA⁻ CD27⁻ CD4⁺ T-cell subsets, indicating that they are not an exhausted population. In addition, CD45RA⁺ CD27⁻ CD4⁺ T cells have cytotoxic potential as they express high levels of granzyme B and perforin. CD4⁺ memory T cells re-expressing CD45RA can be generated from the CD45RA⁻ CD27⁺ population by the addition of IL-7 and during this process these cells down-regulated expression of IL-7R and Bcl-2 and so resemble their counterparts in vivo. Finally we showed that the proportion of CD45RA⁺ CD27⁻ CD4⁺ T cells of multiple specificities was significantly higher in the bone marrow than the blood of the same individuals, suggesting that this may be a site where these cells are generated.     

CD57+ T lymphocytes are derived from CD57− precursors by differentiation occurring in late immune responses

CD3⁺ T cells expressing the 110-kDa CD57 antigen are found in survivors of renal, cardiac and bone marrow transplants, in patients with acquired immune deficiency syndrome and in patients with rheumatoid arthritis. They are also present in normal individuals and expand upon ageing. They do not grow in culture and their role in the immune response is poorly understood. The expression of the various isoforms of the leukocyte common antigen (CD45) identifies a spectrum of differentiation in CD4⁺ and CD8⁺ T cells ranging from naive (CD45RA⁺CD45RB^brightCD45RO^?) through early primed cells (CD45RA^?RB^brightRO^dull) to highly differentiated memory cells which are CD45RA^?RB^dullRO^bright. CD45 isoforms expressed by CD57⁺ T cells showed distinct differences between CD4⁺ and CD8⁺ populations, but in each case indicated an advanced state of differentiation. The expression of T cell receptor Vβ families was highly variable between individuals, but both CD57⁺ and CD57^? cells show a full range of the specificities tested. Vβ expression was more closely related within either the CD4⁺ or the CD8⁺ subsets, irrespective of CD57 expression, than between these subsets, suggesting a relationship between CD57⁺ and CD57^? cells within the same T cell pool. This possibility was supported by experiments showing that CD3⁺CD57⁺ lymphocytes were similar to CD3⁺CD57^? T cells in terms of the production of basic T cell cytokines [interleukin (IL)-2, IL-4, and interferon-γ]. Furthermore, in vitro stimulation of CD3⁺CD57^? T cells in secondary mixed leukocyte reaction or by co-culture with IL-2 and IL-4 induced the appearance of CD3⁺CD57⁺ cells with phenotypic and functional similarities to in vivo CD3⁺CD57⁺ cells. These data strongly suggest that the expression of CD57 is a differentiation event which occurs on CD57^? T cells late in the immune response.     

CD4+CD45RA+T cells from adults respond to recall antigens after CD28 ligation

The leukocyte common antigen isoforms CD45RA and CD45RO havelong been used to discriminate human naive and memory T cellsrespectively. This model was largely based on the observationthat CD45RO⁺ T cells respond preferentially to and show a higherfrequency of precursors specific for recall antigens. However,CD45RA⁺ T cells have more stringent requirements for stimulationand standard in vitro assays may favour CD45RO⁺ cells in thisrespect. We tested the hypothesis that CD45RAf T cells respondpoorly to in vitro stimulation with recall antigens becauseof inadequate stimulation rather than a lack of precursors.Limiting dilution analyses (LDA) for tetanus toxoid (lT)-specificT cells were performed in the presence or absence of exogenousantLCD28 antibody. Addition of antLCD28 yielded no proliferationin the absence of specific antigen. The precursor frequencyfor lT in the CD4⁺ CD45RO⁺ population was –1:4000, whilethe frequency of CD4⁺ CD45RA⁺ T cells specific for lT was 4-to >>20-fold lower. Addition of anti-CD28 antibody didnot significantly alter the apparent precursor frequency forCD45RA⁺ cells but yielded an enhancement of the value for CD45RA⁺cells by 3- to >>5-fold. No enhancement of antigen-specificproliferation by antLCD28 was observed with CD45RA⁺ T cellsderived from cord blood, although phytohemagglutinin responsesof these cells were amplified by CD28 antibody. These resultsindicate that conventional LDA underestimate the true precursorfrequency of antigen-specific cells within the adult CD45RA⁺population and support the possibility that a small number ofcells revert from a primed (CD45RO⁺) to an unprimed (CD45RA⁺)state. The majority of memory T cells, however, appear to residein the CD45RO⁺ population     

CD8+ and CD45RA+ human peripheral blood lymphocytes are potent sources of macrophage inflammatory protein 1α, interleukin-8 and RANTES

The chemokines macrophage inflammatory protein 1α (MIP 1α), interleukin-8 (IL-8) and RANTES are potent regulators of leukocyte trafficking. Examination of chemokine secretion by human peripheral blood lymphocytes after stimulation with anti-CD3 or phorbol 12, 13 myristate acetate and ionomycin showed CD8⁺ cells were the dominant source of MIP 1α and RANTES. Although production of MIP 1α and IL-8 were similar in pharmacologically stimulated CD4⁺ CD45RA⁺, CD4⁺ CD45RO⁺, and CD8⁺ CD45RA⁺ cells, the largest amounts of MIP 1α and RANTES were secreted by CD8⁺ CD45RO⁺ lymphocytes. A parallel pattern of prolonged chemokine mRNA expression for at least 18 h after activation was observed in the T cell subsets. These results confirm that human T lymphocytes have a unique capacity for secretion of these three chemokines. In addition, CD8⁺ cells have an unrecognized role in recruiting cells to sites of inflammation, and adult human CD45RA⁺ cells have a physiologically significant secretory capacity.     

Human primary adenotonsillar naïve phenotype CD45RA CD4 T lymphocytes undergo apoptosis upon stimulation with a high concentration of CD3 antibody

Young children need to develop immune tolerance to harmless foreign antigens such as digested nutrients and various inhaled airborne antigens. Because of its anatomical location, pharyngeal adenotonsillar tissue is a potential site for the establishment of this immune tolerance. To characterize possible mechanisms of peripheral immune tolerance, we studied human primary adenotonsillar naïve phenotype CD45RA⁺ CD4⁺ T cells, which represent cells that have not previously encountered foreign antigens. It was found that these CD45RA⁺ CD4⁺ T cells expressed higher levels of the activation marker CD69 as compared with peripheral blood CD45RA⁺ CD4⁺ T cells. Upon stimulation with a high concentration of CD3 antibody, which mimics the encounter of a high antigen dose, adenotonsillar CD45RA⁺ CD4⁺ T lymphocytes, but not peripheral blood CD45RA⁺ CD4⁺ T cells, underwent apoptosis. After 6 h stimulation with a high concentration of CD3 antibody, over 25% of the cells were apoptotic. Interfering with the Fas–FasL interaction with recombinant Fas or an antibody against Fas-ligand partially inhibited apoptosis. Our study results suggest that high concentrations of antigens, such as various nutrients and airborne antigens, may induce peripheral immune tolerance by selectively deleting naïve phenotype CD45RA⁺ CD4⁺ T cells via T-cell receptor-triggered apoptosis in human adenotonsillar tissue.     

CD45RA expression on γδ and αβ T cells emigrating from the fetal and postnatal thymus

We have compared the expression of CD45RA on αβ and γδ T cells emigrating from the fetal and postnatal thymus. The fetal and postnatal thymus export both CD45RA⁺ and CD45RA^- T cells. The number of γδ⁺CD45RA⁺ T cells was remarkably constant regardless of stage of ontogeny or T cell maturity. Around 5--8% of γδ thymic emigrants, thymocytes and peripheral blood lymphocytes expressed CD45RA in both fetal and postnatal animals. In contrast to γδ T cells, up to one quarter of both fetal and postnatal αβ emigrants expressed CD45RA. Post-thymic maturation of CD45RA expression on αβ emigrants, which occurred both before and after birth, appeared to be antigen independent.     

Comparison of lymphokine secretion and mRNA expression in the CD45RA+ and CD45RO+ subsets of human peripheral blood CD4+ and CD8+ lymphocytes

Flow cytometric analysis of human peripheral blood T lymphocytes demonstrated that the majority of the CD4⁺ cells were CD29⁺ or CD45RO⁺ “mature” cells while the CD8⁺ cells were primarily CD45RA⁺ “naive” cells. After an initial separation into CD4⁺ and CD8⁺ cells and a secondary separation into CD45 subsets, lymphokine secretion was assessed after phorbol 12-myristate 13-acetate and ionomycin or fixed anti-CD3 stimulation. Within the respective CD45 subsets, CD4⁺ cells produced more interleukin (IL)-2, IL-4, and IL-6; but the CD8⁺ cells secreted more interferon-γ and granulocyte/macrophage-colony-stimulating factor. Tumor necrosis factor-α secretion was similar in the matched CD45 subsets. Northern analysis revealed a parallel pattern of lymphokine mRNA expression in the four lymphocyte subsets. These results suggest that human CD8⁺ peripheral blood lymphocytes have a significant capacity to secrete lymphokines, and that the low lymphokine production observed in unseparated CD8⁺ cells reflects the higher percentage of less functional CD45RA⁺ cells.     

Nodal peripheral T-cell lymphomas correspond to distinct mature T-cell populations

Peripheral T‐cell lymphomas (PTCL) have not been successfully correlated with specific developmental stages of reactive T‐cells. Mature T‐cells pass through distinct stages upon antigen encounter. Naïve T‐cells are CD45RA⁺/CD45R0^?/CD27⁺/CCR7⁺. After antigen contact they replace CD45RA expression with CD45R0. The mature T‐cells differentiate to central memory cells, which retain CD27 and CCR7, or to effector memory cells, which lose expression of both molecules depending on the strength of the antigen interaction. In this study, we evaluated lymph node biopsies from eight PTCL—not otherwise specified (PTCL‐NOS), seven angioimmunoblastic T‐cell lymphomas (AILT), and 15 anaplastic large cell lymphomas (ALCL). Detection of tumour cells with antibodies that recognize specific rearranged T‐cell receptor Vβ segments allowed us to investigate the expression of various differentiation‐associated molecules. Results were analysed by hierarchical cluster analysis. All AILT and ALCL showed a homogeneous effector cell phenotype (CD45RA^?/CD45R0⁺/CD27^?), but differed in the cytotoxic and activation markers expressed. Several (5/8) PTCL‐NOS clustered together; these cases all exhibited a CD4⁺ central memory cell phenotype (CD45RA^?/CD45R0⁺/CD27⁺) and four expressed the lymph node homing receptor CCR7. In conclusion, AILT and ALCL tumour cells correspond to different subsets of effector cells, while a subset of PTCL‐NOS correlates with a non‐effector T‐cell population. Copyright © 2006 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Role of CD40 antigen and interleukin-2 in T cell-dependent human B lymphocyte growth

In the present study, we examined the participation of CD40 ligand (L)-CD40 interaction in T cell-dependent B cell responses. To this end, purified B lymphocytes were cultured over irradiated CD4⁺ cloned T cells activated with immobilized anti-CD3 antibody. The anti-CD40 mAb 89 strongly blocked, in a specific fashion, both proliferation and Ig secretion of tonsil B cells. Interestingly, proliferation of surface (s)IgD⁺ B cell was significantly less inhibited by anti-CD40 than that of sIgD^? cells. Preactivated T cells induced B cells to grow and secrete immunoglobulins preferentially in response to IL-2. This contrasts with the CD40 system where B cells are essentially responsive to IL-4 and IL-10 but not to IL-2 alone. Collectively, these data indicate that CD40L-CD40 interaction plays an important role in IL-2-mediated T cell-dependent B cell responses. However, the activation of a subset of sIgD⁺ cells may be independent of this interaction.     

The variable occurrence of CD45RA on CD8+ thymocytes correlates with the presence of Mtv sequences; its expression on other thymocytes is rare

While all thymocytes express CD45, only a small fraction (<3% in mice) bear the high molecular weight isoform, CD45RA. It has been suggested that these cells alone constitute the generative thymocyte lineage and should, therefore, occur within every ontogenic subset. To test this, we determined CD45RA expression among thymocyte subsets defined by CD4 and CD8. In some strains, exemplified by C57BL/Icrf, very few (< 0.2%) Tthymocytes expressed CD45RA and were mostly CD4^?CD8^? or CD4⁺CD8⁺, inconsistent with them constituting the generativelineage. In others, exemplified by BALB/c, CD45RA was expressed on up to 3% of T thymocytes, which were mostly CD4^?CD8⁺. The limited occurrence of CD4^?CD8⁺CD45RA⁺ thymocytes suggests that they are a nonconstitutive subset playing a role in the thymus of only some strains. Their occurrence correlates with that of Mtv proviruses within the mouse genome; however, their T cell receptor V_β repertoire is diverse, suggesting they are not uniquely selected by Mtv superantigens. We propose that they may be mature CD8 T cells, possibly responsible for introducing viral superantigens into the thymus.     

Rapid re-expression of CD45RC on rat CD4 T cells in vitro correlates with a change in function

Rat CD4⁺ T cells are divided phenotypically by the anti-CD45RC monoclonal antibody OX22 into subsets with contrasting functions. Stimulation of T cells in vitro is known to induce a change in isoform from CD45RC⁺ to CD45RC^?. We have investigated the in vitro conditions which promote a switch in isoform in the opposite direction. We observed that a majority of CD45RC^? CD4 T cells (> 90%) spontaneously re-expressed CD45RC during the first 1-3 days of culture in both the presence and absence of alloantigen. The T cells remained CD45RC⁺ when cultured for 7 days in serum-free growth medium. However, alloantigen-activated lymphocytes, expressing the interleukin-2 receptor (IL-2R), down-regulated CD45RC by day 4 and remained CD45RC^? during the course of the experiment. Using mixtures of allotype-marked CD45RC⁺ and CD45RC^?T cells, it was demonstrated that each subset showed comparable survival, IL-2R expression and time courses of activation in response to alloantigen. The repertoire of neither subset was, therefore, deficient in terms of allorecognition. The rapid re-expression of CD45RC in culture was accompanied by a change in function: CD45RC⁺ “converts”, obtained by overnight culture of CD45RC^? T cells, induced significantly higher graft-versus-host responses. Thus, the transition in culture from CD45RC^? to CD45RC⁺ reflects a major functional reprogramming of the cell and not a trivial modulation of a surface antigen.     

Differential response of CD4+ V7+ and CD4+ V7− T cells to T cell receptor-dependent signals: CD4+ V7+ T cells are co-stimulation independent and anti-V7 antibody blocks the induction of anergy by bacterial superantigen

V7 is a novel cell surface glycoprotein that is expressed on 25% of circulating T lymphocytes. This molecule appears to play a critical role in T cell activation based on the observation that a monoclonal anti-V7 antibody inhibits T cell receptor (TCR)-dependent interleukin-2 (IL-2) production and proliferation of T cells. In the current study, CD4⁺ V7+ and CD4⁺ V7? T cells were separated from one another and their response to various stimuli analyzed. Although there were only minor differences between the two subsets in the expression of activation/differentiation markers, including CD45RA and R0 isotypes, when exposed to immobilized anti-CD3 or anti-TCR antibodies in the absence of APC, CD4⁺ V7+ T cells alone produced IL-2 and proliferated vigorously. By contrast, CD4⁺ V7? cells responded poorly to such stimuli, but they recovered their capacity to respond if antigen-presenting cells (APC) or anti-CD28 antibody were added to the cultures. The enhancement of the V7? T cell response by APC appears to be related to augmentation of TCR signals because the effect could be blocked by antibodies against molecules on APC [major histocompatibility (MHC) class II, CD86] that are known to up-regulate such signals through their interaction with counter-receptors on T cells. To assess the role of V7 in a system independent of co-stimulation, CD4⁺ T cells were stimulated with the bacterial superantigens, staphylococcal enterotoxins A and B. The cells responded by proliferating and then becoming anergic. Addition of anti-V7 antibody at the initiation of culture with superantigen did not inhibit cellular proliferation but prevented T cells from becoming anergic, while addition of anti-CD28 antibody had no effect on either proliferation or anergy induction. These results indicate that V7 and CD28 mediate distinct intracellular signals and suggest that V7 functions to preserve T cell reactivity whether the stimulus is mitogenic or anergizing.