Characterization of murine CD160+ CD8+ T lymphocytes

CD160 is an Ig-like glycoprotein expressed on NK, NKT and TCRgammadelta T cells, as well as intestinal intraepithelial T lymphocytes. In addition, a minor subset of CD8(+) but not CD4(+) T cells in the periphery is also known to express CD160, but the subset has not been fully characterized. In this study, we prepared anti-murine CD160 mAbs and investigated the expression profile of CD160 on various subsets of CD8(+) T cells. The amount of CD160 on almost all CD8(+) T cells was increased upon CD3-mediated stimulation in vitro, and soluble CD160 was found to be released. Flow cytometric analysis revealed most CD8(+) T cells expressing CD160 to show a CD44(high) phenotype in vivo. On further analysis, both CD44(high)CD62L(low) effector memory T cells (T(EM)) and CD44(high)CD62L(high) central memory T cells (T(CM)) expressed CD160 at an intermediate level. High levels were evident with recently activated CD8(+) T(EM). Na?ve CD8(+) T cells presumably immediately after stimulation (CD44(low)CD62L(low)CD69(+)) also expressed CD160, but only at a low level. Purified CD160(+) CD8(+) T cells from OT-1 transgenic mice expressing TCR against OVA residues 257-264 presented by H-2K(b) produced IFN-gamma more rapidly than CD160(-) CD8(+) T cells upon antigen stimulation. These results together show that CD160 is expressed on the majority of CD8(+) memory T cells as well as recently activated CD8(+) T cells.     

CD4+CD8+ murine intestinal intraepithelial lymphocytes

We have studied a population of CD4+ intestinal intraepithelial lymphocytes using two-color flow cytometric analyses, and in highly purified fluorescent-activated cell-sorted preparations. Although CD4+ T cells present within the epithelial immune compartment comprised only approximately 10-20% of the total intestinal epithelial lymphoid cells, an unusually high proportion of those CD4+ lymphocytes expressed a CD4+CD8+ phenotype which is rarely encountered in peripheral T cells. By comparison, CD4+ lymphocytes from spleen or lymph nodes existed exclusively as single-positive T cells. Analyses of CD4 and CD8 expression on lymphocytes from Peyer's patches, the lamina propria, and IEL indicated that CD4+CD8+ lymphocytes were unique to the IEL. Using CD4+CD8+ preparations obtained by fluorescent-activated cell sorting, CD4+CD8+ epithelial T cells were found also to express CD3 and Thy-1 surface markers. This heretofore undescribed extrathymic population of double-positive T cells constitutes a unique peripheral T cell subset which may be involved in intestinal T cell maturation and development, or could represent a highly specialized effector population.     

Differential effects of CD4 and CD8 engagement on the development of cytokine profiles of murine CD4+ and CD8+ T lymphocytes

A simple culture system devoid of antigen-presenting cells was used to examine the ability of immobilized antibodies to lymphocyte function-associated antigen-1 (LFA-1) (CD11a), CD28 and CD4 or CD8 to modulate the responses of normal murine CD4+ and CD8+ lymph node T cells to immobilized anti-CD3 antibody and interleukin-2 (IL-2). All the antibodies enhanced proliferative responses to limiting anti-CD3 antibody. Both CD4+ and CD8+ cells produced substantial titres of IL-3 and interferon-gamma (IFN-gamma) in primary and secondary cultures regardless of the coactivating antibodies used for priming. By contrast, the combination of anti-CD4 with anti-CD3 antibody stimulated significantly higher titres of IL-4 than any other antibody combination in cultures of CD4+ cells. This CD4-dependent IL-4 response was induced in CD4+ T cells of naive (CD44low) phenotype and was similar in magnitude to the response induced by exogenous IL-4 but, unlike the latter, was not associated with elevated IL-3 synthesis. A comparable effect of anti-CD8 antibodies on CD8+ cells was not observed: although IL-4 production by CD8+ cells was induced by exogenous IL-4, it was not detected following coactivation with anti-CD8 or any other antibodies. We conclude that anti-CD4 antibody is a potent inducer of IL-4-secreting CD4+ T cells whose effects can be distinguished from those of anti-CD8 antibody on CD8+ T cells and from those of IL-4 on either subset.     

免疫磁珠负性分离纯化小鼠脾脏CD8+ T细胞

目的 探讨小鼠脾脏CD8 T细胞的免疫磁珠负性分选方法,并对分选后所得细胞进行纯度、活力及功能检测.方法 以免疫磁珠负性分选法从小鼠脾脏细胞中分离CD8 T细胞,流式细胞术检测所得细胞的纯度,台盼蓝检测细胞活力并用ConA刺激检测增殖能力. 结果 经过流式细胞仪测定免疫磁珠负性分选后的小鼠脾脏CD8 T细胞纯度达到(91.6±3.6)%,台盼兰染色细胞活力为(94.9±3.2)%,ConA刺激72 h后有(56.3±1.7)%的细胞增殖.结论 免疫磁珠负性分选法能够分选出高纯度的CD8 T细胞,并且不影响分选靶细胞的细胞活力和功能.     

Role of CD8+ and CD4+ T lymphocytes in jejunal mucosal injury during murine giardiasis

T-cell-mediated pathogenesis has been documented in various idiopathic and microbially induced intestinal disorders. Diffuse microvillous shortening seen in giardiasis is responsible for disaccharidase insufficiencies and malabsorption of electrolytes, nutrients, and water. Other mucosal changes include crypt hyperplasia and increased numbers of intraepithelial lymphocytes (IEL). A recent report using an athymic mouse model of infection showed that these epithelial injuries were dependent on T cells. The aim of the present study was to identify which subset of superior mesenteric lymph node (SMLN) T cells were responsible for mucosal alterations in giardiasis. CD4+ and CD8+ T cells, as well as whole lymphocyte populations, were isolated from SMLN of Giardia muris-infected mice for adoptive transfer. Jejunal segments of recipient mice were assessed for brush border ultrastructure, sucrase activity, crypt/villus ratio, and IEL numbers. Mice that received enriched CD8+ and whole SMLN lymphocytes, but not CD4+ T cells, from infected donors showed diffuse shortening of microvilli, loss of brush border surface area, impaired sucrase activity, and increased crypt/villus ratios compared to respective controls. Transfer of whole SMLN lymphocytes, as well as enriched CD4+ or CD8+ T cells, from infected donors led to increased IEL numbers in the recipient jejunum. The findings indicate that loss of intestinal brush border surface area, reduced disaccharidase activities, and increased crypt/villus ratios in giardiasis are mediated by CD8+ T cells, whereas both CD8+ and CD4+ SMLN T cells regulate the influx of IEL.     

An antigen expressed by murine CD8+ T cells and activated B cells

A monoclonal antibody, H1F5, is described that reacts with a subset of Lyt-2 (CD8) mouse T cells and LPS-activated B cells. In both lymph nodes and spleen of BALB/c mice, the H1F5 antigen is coexpressed approximately on 20%-30% of the CD8+ T cells and approximately on 91% of LPS-activated B cells. In the thymus, few cells (less than 1%) are positive for the marker, but no correlation could be demonstrated with markers for mature T cells such as MEL-14 and PNA expression. Elimination of H1F5+ cells by complement lysis led to a 30%-50% reduction of specific lysis as measured in a primary allo CTL, indicating that the cytotoxic effector cells are injured. The relationship of this marker and other antigenic determinants on lymphocytes is discussed.     

Upregulation of CD4 on CD8+ T cells: CD4dimCD8bright T cells constitute an activated phenotype of CD8+ T cells

Aside from an intermediate stage in thymic T-cell development, the expression of CD4 and CD8 is generally thought to be mutually exclusive, associated with helper or cytotoxic T-cell functions, respectively. Stimulation of CD8+ T cells, however, induces the de novo expression of CD4. We demonstrate that while superantigen (staphylococcal enterotoxin B, SEB) and anti-CD3/CD28 costimulation of purified CD8+ T cells induced the expression of CD4 on CD8+ T cells by 30 and 17%, respectively, phytohaemagglutinin (PHA) stimulation did not induce CD4 expression on purified CD8+ T cells but significantly induced the expression of both CD4 on CD8 (CD4dimCD8bright) and CD8 on CD4 (CD4brightCD8dim) T cells in unfractionated peripheral blood mononuclear cells (PBMC). The level of the PHA-mediated induction of CD4dimCD8bright and CD4brightCD8dim was at 27 and 17%, respectively. Depletion of CD4+ T cells from PBMC abrogated this PHA-mediated effect. Autologous CD4+ and CD8+ T-cell co-cultures in the presence of PHA induced this CD4dimCD8bright T-cell expression by 33%, demonstrating a role for CD4 cells in the PHA-mediated induction of the double positive cells. The induction of CD4dimCD8bright was independent of a soluble factor(s). Phenotypic analysis of CD4dimCD8bright T cells indicated significantly higher levels of CD95, CD25, CD38, CD69, CD28, and CD45RO expression than their CD8+CD4- counterparts. CD4dimCD8bright T cells were also negative for CD1a expression and were predominantly T-cell receptor (TCR) alphabeta cells. Our data demonstrate that CD4dimCD8bright T cells are an activated phenotype of CD8+ T cells and suggest that CD4 upregulation on CD8+ T cells may function as an additional marker to identify activated CD8+ T cells.     

Human CD4+ and CD8+ T lymphocytes are both cytotoxic to Toxoplasma gondii-infected cells.

Studies to determine if Toxoplasma gondii-specific human T cells lyse parasite-infected cells have yielded conflicting results. Furthermore, attempts to obtain human cytotoxic CD8+ T lymphocytes have been difficult because of the lack of a reproducible system for their generation. By using paraformaldehyde-fixed, T. gondii-infected peripheral blood mononuclear cells as antigen-presenting cells, we developed a method whereby T. gondii-specific T-cell lines can be reproducibly generated. Six T. gondii-specific T-cell lines were generated from an individual chronically infected with T. gondii. Cytofluorometric analysis of these lines revealed > 99% CD3+, 85 to 95% CD3+ alpha beta T-cell-receptor-positive (TCR+), 5 to 9% CD3+ gamma delta TCR+, 50 to 70% CD4+, and 20 to 40% CD8+ cells when cells were examined during the first 3 weeks of stimulation and >99% CD3+, >99% CD3+ alpha beta TCR+, < 1% CD3+ gamma delta TCR+, 20 to 40% CD4+, and 60 to 80% CD8+ cells when cells were examined between 5 and 11 weeks. Both CD4+ and CD8+ T cells had remarkable cytotoxic activity against T. gondii-infected target cells (30 to 50% specific Cr release at an effector-to-target ratio of 30:1) but not against uninfected target cells ( < 10% at an effector-to-target ratio of 30:1). Cytotoxic activity by the whole T-cell lines was not T. gondii strain specific. Whole T-cell lines were cytotoxic for target cells infected with the C56 and ME49 strains and the RH strain (which was used to infect peripheral blood mononuclear cells). T. gondii-specific T-cell lines displayed the predominant expression of V beta 7 TCR. The CDR3 regions of the V beta 7 TCRs of these T-cell lines showed a striking degree of sequence identity (oligoclonality). T-cell lines obtained by the method reporter here can be used to characterize functional activity of T-lymphocyte subsets in humans infected with T. gondii.     

Activated CD4+ CD25+ T cells suppress antigen-specific CD4+ and CD8+ T cells but induce a suppressive phenotype only in CD4+ T cells

CD4(+) CD25(+) regulatory T cells are increasingly recognized as central players in the regulation of immune responses. In vitro studies have mostly employed allogeneic or polyclonal responses to monitor suppression. Little is known about the ability of CD4(+) CD25(+) regulatory T cells to suppress antigen-specific immune responses in humans. It has been previously shown that CD4(+) CD25(+) regulatory T cells anergize CD4(+) T cells and turn them into suppressor T cells. In the present study we demonstrate for the first time in humans that CD4(+) CD25(+) T cells are able to inhibit the proliferation and cytokine production of antigen specific CD4(+) and CD8(+) T cells. This suppression only occurs when CD4(+) CD25(+) T cells are preactivated. Furthermore, we could demonstrate that CD4(+) T-cell clones stop secreting interferon-gamma (IFN-gamma), start to produce interleukin-10 and transforming growth factor-beta after coculture with preactivated CD4(+) CD25(+) T cells and become suppressive themselves. Surprisingly preactivated CD4(+) CD25(+) T cells affect CD8(+) T cells differently, leading to reduced proliferation and reduced production of IFN-gamma. This effect is sustained and cannot be reverted by exogenous interleukin-2. Yet CD8(+) T cells, unlike CD4(+) T cells do not start to produce immunoregulatory cytokines and do not become suppressive after coculture with CD4(+) CD25(+) T cells.     

Selection of CMV-specific CD8+ and CD4+ T cells by mini-EBV-transformed B cell lines

Efficient protocols to generate cytomegalovirus (CMV)-specific T cells are required for adoptive immunotherapy. Recombinant Epstein-Barr virus (EBV) vectors called mini-EBV can be used to establish permanent B cell lines in a single step, which present the CMV antigen pp65 in a constitutive manner. These B cell lines, coined pp65 mini-LCL, were successfully used to reactivate and expand CMV-specific cytotoxic T cells. Here we evaluate this pp65 mini-EBV system in closer detail, focusing on (1) the quantification of T cells with specific effector function and (2) the identification of CMV-specific CD4(+) helper T cells. The co-expansion of various functional CMV epitope specificities was demonstrated by IFN-gamma enzyme-linked immunospot assay (ELISPOT) assays and HLA-peptide tetramer staining. Single-cell cloning resulted in both CD4(+) and CD8(+) T cell clones, the majority of which was CMV specific. Thus, mini-LCL present the pp65 antigen on HLA class I and II, mobilizing both arms of the T cell response. Using a peptide library covering the pp65 sequence for further analysis of T cell clones, we identified new pp65 CD8(+) and CD4(+) T cell epitopes.     

Regulation of histamine synthesis in mouse CD4+ and CD8+ T lymphocytes

OBJECTIVES: Previously, we have shown that mouse T lymphocytes produce de novo histamine in response to mitogens. The aim of this study was to examine which subsets of T cells produce histamine and to clarify the regulatory mechanisms of the reaction. MATERIALS: CD4+ and CD8+ T lymphocytes were separated from spleen cells of mast cell-deficient WBB6/F1 (W/Wv) mice using anti-CD4- and anti-CD8-coupled magnetic beads, respectively. RESULTS: Both CD4+ T cells and CD8+ T cells released histamine when treated with Con A as a function of incubation time. Since histamine bound to each cell fraction was negligible before and after the treatment, it is highly likely that this indicates de novo synthesis of histamine by these cells. Granulocyte/macrophage colony-stimulating factor (GM-CSF) or IL-3 strongly enhanced the Con A-induced histamine formation. IL-1-alpha also potentiated the Con A-dependent histamine production. Dexamethasone, but not progesterone, significantly inhibited the Con A-dependent as well as Con A-independent histamine synthesis. Both GM-CSF and IL-3 caused a marked accumulation of histidine decarboxylase (HDC, EC 4.11.22) mRNAs in the cells. CONCLUSIONS: These results suggest that GM-CSF and IL-3 enhance histamine synthesis in CD4+ T cells and CD8+ T cells.     

供体凋亡淋巴细胞预输注对猪肝移植受体CD4+T、CD8+T、CD4+CD25+调节性T细胞的影响

背景：凋亡细胞能够主动调节机体的免疫功能,并能通过调节机体细胞免疫和体液免疫的途径诱导免疫耐受,但这些结果只在大鼠肝脏移植模型中证实。 目的：探讨通过⁶⁰Co γ射线体外处理后的供体淋巴细胞预输注诱导猪肝移植特异性免疫耐受的作用中,对淋巴细胞亚群的影响。 方法：建立非转流小型猪原位肝移植模型。将受体猪随机摸球法均分为2组：空白对照组,受体猪无特殊处理,行肝移植;淋巴细胞组：受体猪在肝移植前7 d经耳静脉注射⁶⁰Co γ射线处理过的5×10⁸个供体淋巴细胞。观察两组受体猪移植后的存活时间,移植后T淋巴细胞亚型CD4⁺T、CD8⁺T、CD4⁺CD25⁺Tr变化及病理。 结果与结论：移植后3 d,两组病理活检均呈急性中、重度排斥反应;移植后6 d,两组均呈急性重度排斥反应。移植后1,3,6 d CD4⁺T、CD8⁺T、CD4⁺CD25⁺Tr升降趋势,两组间差异无显著意义(P > 0.05)。提示,⁶⁰Co γ射线体外处理过的淋巴细胞预输注未能够诱导猪同种异体肝移植特异性免疫耐受,未能引起T淋巴细胞亚群变化有关。     

Phenotypic discrimination between thymic and extrathymic CD4-CD8- and CD4+CD8+ porcine T lymphocytes

The composition of the T lymphocyte population in swine is special in that in addition to the CD4-CD8+ subpopulations, CD4-CD8- and CD4+CD8- and CD4+CD8+ subpopulations are prominent in the peripheral circulating as well as in the resident T lymphocyte pools. Since the same phenotypes are characteristic of thymic populations, it was asked whether the unusual distribution in swine may result from an emigration of thymic precursor phenotypes to the periphery. This explanation was refuted, as all thymic subpopulations were found to express CD1, albeit with differences in antigen density, whereas all extrathymic subpopulations lack CD1. The cellular distribution of CD2 in swine is without precedent among all species studied. Whereas in sheep and cattle the extrathymic CD4-CD8- subpopulation is known to entirely lack CD2 and to have a low propensity for homing to lymphoid tissues, the CD4-CD8- subpopulation in swine splits into CD2+ and CD2- subsets, both of which do reside in lymphoid tissues. While CD2+CD4-CD8- T lymphocytes are rare in the circulating pool, this subset accumulates in spleen and lymph nodes. This may indicate a role for CD2 in homing. Thus the species swine is immunologically unique, not only because of having CD1-CD2+CD4+CD8+ T lymphocytes in the periphery, but also with regard to subdivision and homing behavior of its CD4-CD8- T lymphocyte subpopulation.     

CD4+CD25+ T regulatory cells inhibit cytotoxic activity of T CD8+ and NK lymphocytes in the direct cell-to-cell interaction

There are reports suggesting an influence of CD4(+)CD25(+) T regulatory cells (Treg) on cytotoxic lymphocytes. The aim of the study was to evaluate such an influence. Cytotoxic activity was examined in the cultures of peripheral blood mononuclear cells (PBMC) as well as in the cultures of separate T CD8(+) or NK cells mixed with Treg and other subpopulations of PBMC. We found that the production of IFNgamma, perforin and cytotoxic activity of T CD8(+) or NK cells were decreased in the presence of Treg, however, the percentage of conjugates formed by cytotoxic cells with target cells during cytotoxic reaction was decreased only in the cultures of T CD8(+) cells. Inhibition of the cytotoxic reactions in the presence of Treg cells was found to be associated with the generation of conglomerates formed by CD4(+)CD25(+) and the cytotoxic cells, as observed under the fluorescence microscope. Treg produced IL10 when mixed with the cytotoxic lymphocytes, however, an addition of anti-IL10 mAb into the cultures did not affect the results. It is concluded that Treg were able to inhibit both T CD8+ and NK lymphocyte cytotoxic activities in a direct cell-to-cell interaction. Treg decreased the number of T CD8+ cells attached to the target cells, while the mechanism underlying a decrease in NK cytotoxicity remained unclear.     

Circulating CD4+CD8+ T lymphocytes in patients with Kawasaki disease

We serially monitored cell surface antigen expression on mononuclear cells in peripheral blood isolated from patients with Kawasaki disease (KD), and found, for the first time, that a markedly increased number of CD4⁺CD8⁺ T lymphocytes was present in some of the patients (11 of the 24 cases). The cases of five of these 11 patients were complicated with coronary artery lesion (CAL); the 13 patients with normal numbers of CD4⁺CD8⁺ T lymphocytes did not have CAL. The patients' age, sex and grade of systemic inflammation evaluated by peripheral leucocyte count and serum C-reactive protein levels were not correlated to the number of CD4⁺CD8⁺ T lymphocytes. Other cell surface antigen characteristics of the CD4⁺CD8⁺ T lymphocytes included CD3⁺, CD45RA⁺, CD45RO⁺, CD16^?, and HLA-DR⁺. These results indicate that the surface antigen characteristics of the KD peripheral blood examined were the same as those of Epstein–Barr virus infection without CD45RA⁺. These findings provide useful information for the analysis of the pathogenesis of KD.     

Characterization of CD4- CD8- CD3+ T-cell receptor-alphabeta+ T cells in murine cytomegalovirus infection

In this study, we have investigated that after the intraperitoneal infection with murine cytomegalovirus (MCMV), the CD3+ CD4- CD8-(double negative; DN) T-cell receptor (TCR)alphabeta+ T cells increased in peritoneal cavity, liver and spleen in both resistant C57BL/6 and susceptible BALB/c mice. The total cellular population of these cells showed peak levels around day 5 after infection in all the three investigated organs and the following phenotypical and functional characteristics emerged. The peritoneal DN TCRalphabeta+ T cells expressed highly skewed TCRVbeta8 on day 5 after infection compared with the uninfected mice, but those in spleen and liver showed moderate and low skewed TCRVbeta8, respectively. The percentages of NK1.1+ DN TCRalphabeta+ T cells gradually decreased as did modulation of some of their activation markers consistent with an activated cell phenotype. The peritoneal DN TCRalphabeta+ T cells on day 5 after infection expressed the genes of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha, Eta-1 (early T-cell activation-1) and MCP-1 (monocyte chemoattractant protein 1) but lacked expression of interleukin-4 (IL-4). After in vitro stimulation with phorbol 12-myristate 13-acetate and calcium ionophore in the presence of Brefeldin A, higher frequencies of intracellular IFN-gamma+ DN TCRalphabeta+ T cells were detected in all three investigated organs of infected mice compared with those of uninfected mice. Stimulation of peritoneal DN TCRalphabeta+ T cells with plate-bound anti-TCRbeta monoclonal antibodies showed proliferation and also produced IFN-gamma but not IL-4. These results suggest that DN TCRalphabeta+ T cells were activated and may have an antiviral effect through producing IFN-gamma and some macrophage-activating factors during an early phase of MCMV infection.     

Generation of peptide-specific CD8+ T cells by phytohemagglutinin-stimulated antigen-mRNA-transduced CD4+ T cells

Functional analysis of antigen-specific CD8(+) T cells is important for understanding the immune response in various immunological disorders. To analyze CD8(+) T cell responses to a variety of antigens with no readily defined peptides available, we developed a system using CD4(+) phytohemagglutinin (PHA) blasts transduced with mRNA for antigen molecules. CD4(+) PHA blasts express MHC class I and II, and also CD80 and CD86 and are thus expected to serve as potent antigen presenting cells. EGFP mRNA could be transduced into and the protein expressed by more than 90% of either LCL or CD4(+) PHA blasts. Its expression stably persisted for more than 2 weeks after transduction. In experiments with HLA-A*2402 restricted CD8(+) CTL clones for either EBNA3A or a cancer-testis antigen, SAGE, mRNA-transduced lymphoid cells were appropriate target cells in ELISPOT assays or (51)Cr releasing assays. Finally, using CD4(+) PHA blasts transduced with mRNA of a cancer-testis antigen MAGE-A4, we successfully generated specific CTL clones that recognized a novel HLA-B*4002 restricted epitope, MAGE-A4(223-231). Messenger RNA-transduced CD4(+) PHA blasts are thus useful antigen presenting cells for analysis of CD8(+) T cell responses and induction of specific T cells for potential immunotherapy.     

Antigen-specific CD8+ T cells inhibit IgE responses and interleukin-4 production by CD4+ T cells

There is a growing body of evidence which suggests that CD8⁺ T cells play an important part in regulating the IgE response to non-replicating antigens. In this study we have systematically investigated their role in the regulation of IgE and of CD4⁺ T cell responses to ovalbumin (OVA) by CD8⁺ T cell depletion in vivo. Following intraperitoneal immunization with alum-precipitated OVA, OVA-specific T cell responses were detected in the spleen and depletion of CD8⁺ T cells in vitro significantly enhanced the proliferative response to OVA. Depletion of CD8⁺ T cells in vivo 7 days after immunization failed to enhance IgE production, while depletion of CD8⁺ T cells on days 12–18 greatly enhanced the IgE response, which rose to 26 μ/ml following a second injection of anti-CD8 on day 35 and remained in excess of 1 μ/ml over 300 days afterwards. Reconstitution on day 21 of rats CD8-depleted on day 12 with purified CD8⁺ T cells from animals immunized on day 12 completely inhib ited the IgE response. This effect was antigen specific; CD8⁺ T cells from OVA-primed animals had little effect on the IgE response of bovine serum albumin immunized rats. In vivo, CD8⁺ T cell depletion decreased interferon (IFN)-γ production but enhanced interleukin (IL)-4 production by OVA-stimulated splenic CD4⁺ T cells. Furthermore, CD8⁺ T cell depletion and addition of anti-IFN-γ antibody enhanced IgE production in vitro in an IL-4-supplemented mixed lymphocyte reaction. These data clearly show that antigen-specific CD8⁺ T cells inhibit IgE in the immune response to non-replicating antigens. The data indicate two possible mechanisms: first, CD8⁺ T cells have direct inhibitory effects on switching to IgE in B cells and second, they inhibit OVA-specific IL-4 production but enhance IFN-γ production by CD4⁺ T cells.     

CD8 T cell priming by B lymphocytes is CD4 help dependent

While it is generally accepted that B lymphocytes can present antigen and activate CD4 T cells, priming of CD8 T cells by B lymphocytes remains controversial. Recently, we showed that mice injected with genetically programmed B lymphocytes generate antigen specific CD4 and CD8 T cell responses in vivo that could also be induced in mice lacking functional dendritic cells. To gain further insights into the requirements for T cell priming by antigen-presenting B lymphocytes, in vitro experiments were performed using ovalbumin (OVA) and OVA-specific TCR-transgenic CD4 and CD8 T cells. We found that while B lymphocytes can directly prime CD4 T cells, the activation of CD8 T cells requires T cell help. Transfer experiments show that help can either be contact dependent or be mediated by soluble factors in the supernatants of activated OVA-specific CD4 T cells. Furthermore, the effect of activated CD4 T cells can be replaced by soluble recombinant IL-4. Collectively, the data show the existence of different requirements for priming of CD4 and CD8 T cells and point to the previously unappreciated fact that the induction of CD8 T cell responses by B lymphocytes requires T cell help.     

Rho GTPase-mediated pathways in mature CD4+ T cells

Effective immune responses require the appropriate activation and differentiation of peripheral CD4(+) T cells. These processes need to be followed by the timely elimination of the responding T cells in order to restore T cell homeostasis. Defects in the appropriate regulation of T cell activation, expansion, and survival underlie the pathogenesis of many autoimmune disorders including SLE. The molecular machinery employed by T cells to properly control these processes and prevent the onset of autoimmunity has not been fully elucidated. Rho GTPases (which include the Rac, Cdc42, and Rho subfamilies) are molecular switches that control a wide range of cellular processes. Their fundamental role in biology is due to their ability to regulate both cytoskeletal dynamics and a large number of signal transduction pathways. Activation of Rho GTPases is now recognized as a key event in the coordination of immune responses and, particularly, in the activation of T cells. In this review, we will first provide an overview of the role of Rho GTPase-mediated pathways in mature CD4(+) T cells and then we will discuss recent studies, which suggest that deregulation of these pathways may play a role in the pathogenesis of SLE.