Receptors for the FC Portion of Immunoglobulins (FCR) on Murine Oral Mucosal T Cells

The incidence and distribution of immunoglobulin receptors on oral mucosal T cells were investigated. Enrichment of either Thy-1.2, L3T4 or Lyt-2.2-positive cells was achieved by the use of a panning procedure following cell extraction by an optimized digestion method that preserved all three T-cell markers. The percentage of cells possessing Fc receptors was determined by using immunoglobulin-coated (IgM, IgG or IgA) fluorescent microspheres in a multipoint rosetting assay. We report that approximately 60% of Thy-1.2, L3T4 and Lyt-2.2 positive cells bear FcyR whereas less than 5% of T cells of any subset bear FcaR or FcjiR. In frozen tissue sections, FcyR+ cells were mainly scattered throughout the basal and suprabasal epithelium and were observed at a lower frequency in the minor salivary gland network. From their distribution, it is anticipated that FcyR+ cells may be involved in the surveillance of the epithelium while the minor FcocR+ L3T4+ T lymphocyte population may promote the expression of slgA by resident slgM-bearing B cells, and their differentiation into IgA plasma cells.     

Receptors for the Fc portion of immunoglobulins (FcR) on murine oral mucosal T cells

The incidence and distribution of immunoglobulin receptors on oral mucosal T cells were investigated. Enrichment of either Thy-1.2, L3T4 or Lyt-2.2-positive cells was achieved by the use of a panning procedure following cell extraction by an optimized digestion method that preserved all three T-cell markers. The percentage of cells possessing Fc receptors was determined by using immunoglobulin-coated (IgM, IgG or IgA) fluorescent microspheres in a multipoint rosetting assay. We report that approximately 60% of Thy-1.2, L3T4 and Lyt-2.2 positive cells bear Fc gamma R whereas less than 5% of T cells of any subset bear Fc alpha R or Fc mu R. In frozen tissue sections, Fc gamma R+ cells were mainly scattered throughout the basal and suprabasal epithelium and were observed at a lower frequency in the minor salivary gland network. From their distribution, it is anticipated that Fc gamma R+ cells may be involved in the surveillance of the epithelium while the minor Fc alpha R+ L3T4+ T lymphocyte population may promote the expression of sIgA by resident sIgM-bearing B cells, and their differentiation into IgA plasma cells.     

Tissue distribution and cytofluorometric analysis of oral mucosal T cells in the BALB/c mouse

The incidence and distribution of Thy-1.2+, Lyt-2.2+ and L3T4+ cells in the murine oral mucosa were investigated using qualitative and quantitative approaches. From immunostaining of frozen tissue sections, it appeared that the majority of oral T cells are located either in the epithelium or within the minor salivary gland network. The occurrence of Thy-1.2+, L3T4+ and Lyt-2.2+ cells at these sites points to two strategic lines of defence in the event of mucosal infections or aggression. A quantitative analysis of oral T-cell subsets was made possible by optimizing an enzymatic digestion procedure which preserves all three T-cell surface markers. Flow cytometric analysis of oral mucosal cells demonstrated that the helper phenotype is about twice as numerous as the cytotoxic/suppressor phenotype in the mucosa. Furthermore, in single cell suspensions, virtually all Thy-1+ cells were either L3T4+ or Lyt-2.2+ in the mucosa and in the spleen. From this frequency analysis and our previous studies, we conclude that T cells are a major component of the oral immune system, being 2-3 times as numerous as B cells or macrophages. Present data on the spatial distribution and characteristic ratio of T-cell subsets assess the basal activity of the local T-cell populations in healthy animals and lay the basis for comparative studies of both qualitative and quantitative variations occurring during mucosal infections or autoimmune reactions.     

Tissue distribution and cytofluorometric analysis of oral mucosal T cells in the balb/c mouse

The incidence and distribution of Thy-1.2⁺, Lyt-2.2⁺ and L3T4⁺ cells in the murine oral mucosa were investigated using qualitative and quantitative approaches. From immunostaining of frozen tissue sections, it appeared that the majority of oral T cells are located either in the epithelium or within the minor salivary gland network. The occurrence of Thy-1.2⁺, L3T4⁺ and Lyt-2.2⁺ cells at these sites points to two strategic lines of defence in the event of mucosal infections or aggression. A quantitative analysis of oral T-cell subsets was made possible by optimizing an enzymatic digestion procedure which preserves all three T-cell surface markers. Flow cytometric analysis of oral mucosal cells demonstrated that the helper phenotype is about twice as numerous as the cytotoxic/suppressor phenotype in the mucosa. Furthermore, in single cell suspensions, virtually all Thy-1⁺ cells were either L3T4⁺ or Lyt-2.2⁺ in the mucosa and in the spleen. From this frequency analysis and our previous studies, we conclude that T cells are a major component of the oral immune system, being 2–3 times as numerous as B cells or macrophages. Present data on the spatial distribution and characteristic ratio of T-cell subsets assess the basal activity of the local T-cell populations in healthy animals and lay the basis for comparative studies of both qualitative and quantitative variations occurring during mucosal infections or autoimmune reactions.     

Studies on cell surface antigens of mouse leukemic and normal lymphocytes. IV. Functional studies on mouse T lymphocyte subpopulations. B. Lyt phenotype of cytotoxic T lymphocytes and their precursors in B6-Lyt-1.1 mice.

Lyt phenotype of in vitro generated alloreactive cytotoxic T lymphocytes (CTL) and their precursors in B6-Lyt-1.1 (Thy-1.2, Lyt-1.1, Lyt-2.2) congenic strain of mice was studied. The generation of CTL in vitro was completely abrogated by pretreatment of responder cells with antisera to Thy-1.2, Lyt-1.1 and Lyt-2.2 antigens and complement. Mixing of anti-Lyt-1.1-pretreated cells with anti-Lyt-2.2-pretreated cells did not restore CTL generation indicating that both Lyt antigens are expressed on the same precursor cell population. The effect of anti-Lyt sera was specific because the generation of CTL was prevented only when cells from strains possessing appropriate Lyt alleles were pretreated. CTL were eliminated by lysis with anti-Thy-1.2 serum and strongly reduced by anti-Lyt-1.1 and anti-Lyt. 2.2 sera. Nevertheless, a small but significant proportion of CTL was insensitive to lysis with anti-Lyt sera. These data indicate that a phenotype of precursor cells and of majority of CTL is Thy-1.2+ Lyt-1.1+ Lyt-2.2+.     

Identification of intrathymic T progenitor cells by expression of Thy-1, IL2 receptor and CD3

Immature (L3T4-/Lyt-2- "double-negative") thymocytes were separated into several functionally distinct fractions based on their expression of IL2 receptors, Thy-1 and CD3. The majority (60-70%) of double-negative thymocytes in young adult mice lack detectable IL2 receptor expression, have high levels of Thy-1 and rapidly "progress" to a L3T4+ or L3T4+/Lyt-2+ stage when cultured for 20 h in simple medium. In contrast, the IL2 receptor-positive fraction retains the double-negative phenotype for as long as it survives in culture and addition of IL2 has little or no effect on such cells. IL2 does generate strong proliferation from a fraction of cells expressing low levels of Thy-1, but not detectable IL2 receptors. Such culture generates an unusual population of double-negative cells that expresses the pan-B cell molecule B220 and which kill both the NK target cell line YAC-1 and the NK-resistant line EL4. This Thy-1-low fraction includes all of the double-negative thymocytes capable of T cell reconstitution. Thy-1-low fraction could be further separated into two populations with regards to CD3 expression. CD3- but not CD3+ population could reconstitute mature T cells, indicating that Thy-1-low, IL2R- and CD3- cells are the most enriched population of intrathymic T cell progenitors.     

CD4-/CD8-T cells: amplification in spleens of mice following in vivo treatment with monoclonal antibody anti-L3T4

Amplification of L3T4-/Ly-2-(CD 4-/CD 8-) T cells following in vivo administration of anti-L3T4 monoclonal antibody was examined in the spleen of mice by flow cytometry and immunohistochemistry. BALB/c mice were given 4-7 weekly injections of either anti-L3T4 (1 mg/week) or phosphate-buffered saline (control group), and dispersed spleen cells and tissue sections analyzed for the presence of Thy-1.2+, L3T4+, or Ly-2+ cells, and for the absence of both L3T4 and Ly-2 on Thy-1.2+ cells. Prior to treatment, L3T4+ and Ly-2+ cells accounted for virtually all Thy-1.2+ cells in approximately a 2:1 ratio. Following anti-L3T4 treatment, L3T4+ cells were depleted, and Ly-2+ cells accounted for about 2/3 of the Thy-1.2+ cells. A population of L3T4-/Ly-2- T cells was generated that accounted for 20-30% of the Thy-1.2+ cells, accounted for most of the Thy-1.2+ cells in red pulp, and was also present among the predominant Ly-2+ cells in periarteriolar sheaths.     

Characterization of a CD4(L3T4)-positive cytotoxic T cell clone that is restricted by class I major histocompatibility complex antigen on FBL-3 tumor cell

An L3T4(CD4)+ CTL clone specific for Friend virus-induced tumor FBL-3 was isolated, characterized and compared with a conventional Lyt-2(CD8)+ CTL clone. This clone L3.1 was obtained from the limiting dilution culture of splenic MLTC cells from a CB6F1 mouse whose CD8+ T cells had been suppressed by an in vivo injection of anti-Lyt-2.2 mAb. The phenotype of clone L3.1 was sIg-, Thy-1.2+, L3T4(CD4)+, Lyt-2 (CD8)-, and Ia- as determined by flow-cytometry. Northern blot analysis also confirmed that mRNA for L3T4(CD4), but not for Lyt-2 (CD8) was present in the total RNA of L3.1. The FBL-3-specific killing activity of L3.1 was inhibited by anti-H-2D6 mAb, and the tumor cells did not express class II MHC antigen, indicating that the recognition of tumor antigen by this CD4+ CTL clone was restricted by the class I MHC molecule on the tumor cells. Furthermore, the finding that anti-L3T4(CD4) mAb GK1.5 inhibited the specific and lectin-dependent non-specific cytotoxicity of L3.1 suggested that CD4 molecules on this CTL clone are not ligand (MHC class II)-binding proteins, but are involved in signal transduction.     

Flow microfluorometry analysis of alterations in T-lymphocyte subsets during murine listeriosis

C57BL/6 mice were infected intravenously with 6 X 10(3) Listeria monocytogenes organisms. As early as day 3 of infection, there was a marked reduction in the number of lymphocytes recovered from the peripheral blood, bone marrow, and thymuses of infected animals. Concomitantly, there was an increase in the number of splenic lymphocytes. By day 14, both the total and differential cell counts were similar in both infected and normal animals. Flow microfluorometric studies comparing the Thy-1.2, Lyt-1, Lyt-2, and surface immunoglobulin (SIg) phenotypes of lymphocytes from normal and infected mice were performed. Between days 3 and 5, there was a decrease in the percentage of Thy-1.2+ cells in the spleens of L. monocytogenes-infected animals. Conversely, the percentages of Lyt-1+, Lyt-2+, and SIg+ cells remained constant. At day 7 of infection, the percentage of Thy-1.2+ splenocytes was within normal limits, and at day 10, the percentage of Thy-1.2+ cells was elevated slightly. The absolute numbers of Thy-1.2+ cells were comparable in both infected and normal animals at early stages (days 3 to 5) of L. monocytogenes infection, but there was a marked elevation of Thy-1.2+ splenocytes at days 7 to 14 of infection. Lyt-1+, Lyt-2+, and SIg+ splenocytes increased in absolute numbers as early as day 3 of infection and were still elevated at day 14. Adrenalectomy before infection had no effect on the results obtained, suggesting that these changes were not mediated by endogenous steroids.     

Age-related changes of splenic T cells in mice--a flow cytometric analysis

Splenic T cells of C57BL/6 mice, ranging in age from newborn to 24 months old, were examined by two-colour flow cytometry using monoclonal antibodies (moAbs) to Thy-1, Lyt-1, Lyt-2 and L3T4. Thy-1+ cells in the spleen increased gradually after the birth, and reached a plateau around at 3 months of age, but did not show a significant age-related decline even at 24 months of age. Lyt subpopulations of T cells (Lyt-1+2+, Lyt-1+2-, Lyt-1-2+) showed a proportional increase until 1 month of age, but the onset of their imbalance was observed as early as 3 months of age. The percentage of L3T4+ subpopulation stayed at a relatively constant level throughout life (approx. 55%). At the individual cell level, Lyt-2 antigen was most vulnerable to aging and its membrane surface density showed a prominent decrease in 24-month-old T cells. An apparent decline was observed in the mitogen reactivity and cell-mediated cytolytic T lymphocyte (CTL) activity of old T cells or their subpopulations which were purified by the cell sorter.     

Generation of L3T4-/Ly-2- T cells in Peyer's patches of mice treated with monoclonal antibody against helper T cells

The effect of in vivo administration of anti-L3T4 monoclonal antibody on the generation of an L3T4-/Ly-2- (CD4-/CD8-) population of Thy-1.2+ cells was examined in Peyer's patches of mice by two-color flow cytometry. Female BALB/c mice aged 8 wk were given 4-6 weekly injections of either anti-L3T4 (1 mg/wk) or phosphate-buffered saline (control group), and dispersed Peyer's patch cells analyzed for the presence and absence of L3T4 and Ly-2 on Thy-1.2+ cells. In anti-L3T4 treated mice, L3T4-/Ly-2- T cells accounted for 25-30% of the Thy-1.2+ cells, whereas in control mice these cells represented only 3-4% of the T cells. The remaining 70-75% of the Thy-1.2+ cells after anti-L3T4 treatment were Ly-2+ and not L3T4+. The L3T4-/Ly-2- population of Thy-1.2+ cells is a novel subset which has not been previously found in Peyer's patches and is amplified when helper T cells are depleted.     

Electrophoretic fractionation of murine lymphoid cells. I. Enrichment of peripheral T lymphocyte subsets with distinct surface phenotypes

The purpose of this work was to evaluate the efficiency of free-flow electrophoresis as a method for separating mouse lymphocyte subsets. The surface phenotype of the cells contained in the various fractions collected after electrophoresis of CBA/J lymph node cells was investigated by means of single- and 2-color flow cytofluorometry (FCF) analysis. In agreement with previous works, B cells (sIg+, Thy-1-) were found to segregate in the low mobility (LM) fractions and T cells (sIg-, Thy-1+) in the high-mobility (HM) fractions. While the mean fluorescence intensity of sIg staining did not significantly vary as a function of electrophoretic mobility (EPM) that of Thy-1 staining tended to decrease with increasing EPM. The distribution of Lyt-1+ cells was roughly parallel to that of Thy-1+ cells. However, 2-color FCF analysis suggested the existence, in addition to a major Thy-1+ Lyt-1+ subpopulation, of a minor subset of Thy-1- Lyt-1+ cells. Lyt-2+ cells made up a peak in the cathodic HM region where they were enriched by up to 3-fold, and a trail in the more anodic HM fractions. Two-color FCF analysis showed that all Lyt-2+ cells recovered in these various electrophoretic fractions expressed the Lyt-1 antigen. Taken together, these data demonstrate that free-flow electrophoresis provides a powerful tool for the delineation and substantial enrichment of phenotypically distinct mouse peripheral T cell subsets.     

The role of L3T4+ cells in the pathogenesis of lupus in lpr-bearing mice. I. Defects in the production of interleukins 2 and 3

Mice which bear the lpr gene spontaneously develop autoimmune syndromes characterized by massive expansion of an unusual T cell subset which is phenotypically Thy-1+, L3T4-, Lyt-2-, B220+. The mutant T cells are refractory to stimulation with mitogenic lectins and, by implication, are thought to be solely responsible for the defects in lymphokine production manifested by lpr mice. The contribution of the remaining L3T4+ T cell subset to the latter derangements has not been previously examined and is the focus of this study. We found that abnormalities in concanavalin A-induced interleukin 2 and 3 production in the spleens of MRL-lpr/lpr and C57BL/6.lpr mice occurred in the presence of limited infiltration with B220+, L3T4- T cells. Mixing experiments indicated that B220+ T cells were not suppressive. Furthermore, lpr spleen cells enriched for L3T4+ cells and depleted of sIg+, B220+ and Lyt-2+ cells demonstrated reductions in lymphokine production which were comparable to those seen in unfractionated preparations. Spleen cells from C57BL/6.lpr mice, enriched for L3T4+ cells, were also markedly impaired in a mixed leukocyte reaction in response to stimulator cells from the class II major histocompatibility complex mutant bm12. The results indicate that the aberrations in lymphokine production and proliferation in the spleen cells of lpr mice involve not only B220+ T cells but also L3T4+ cells and suggest a potential role for the L3T4+ subset in the pathogenesis of lupus in lpr-bearing mice.     

Expression of Fc gamma receptors on splenic T cells of mice infected with Plasmodium chabaudi adami

In previous studies, it was shown that mice infected with Plasmodium chabaudi adami have a deficiency in their production of IgG1 immunoglobulin, suggesting isotype-specific immunoregulation. In order to examine this phenomenon in further detail the expression of Fc gamma receptors (Fc gamma R) on T cells obtained from mice infected with P. chabaudi was studied by flow cytometry. There was an increase in the number of splenic T cells which expressed Fc gamma R during infection. At the peak of the acute stage of infection (10-15 days) up to 40% of T cells were positive for Fc gamma R expression. These Fc gamma R were present on about 40% of both Lyt-2+ and L3T4+T cells. The isotype preference of these receptors on control Thy-1+ T cells is IgG1 greater than IgG2b greater than IgG2a as determined by an inhibition assay and fluorescence-activated cell sorter (FACS) analysis. However, 2 to 3 weeks after infection this pattern was altered such that IgG2b and IgG2a represented the major isotypes binding to the Fc gamma R of the L3T4+ T cell. At this stage of infection Fc gamma R on L3T4+ cells fail to bind IgG1. In the Lyt-2% T cells IgG1 and IgG2b remained the best inhibitors. These data suggest that there may be changes in Fc gamma R expression on T cells during infection reflected particularly in a decreased ability of IgG1 to bind to the Fc gamma R of L3T4+ cells.     

Restitution of the thymus in lethally irradiated mice after transplantation of syngeneic or allogeneic bone marrow

The early restitution of the thymus of bone marrow chimeras was investigated by the immunoperoxidase technique using monoclonal antibodies against Thy-1 and Lyt-1, Lyt-2, Lyt-3. Within two weeks, normal thymus histology was restored in mice which received untreated syngeneic BM or syngeneic or allogeneic BM pretreated with SAL (specificed antilymphocytic serum). Irradiation depleted the thymic cortex of small Thy-1+, Lyt-1+2+3+ cells but did not affect a medullary population of medium sized weakly stained Thy-1+, strongly stained Lyt-1+ cells. Preceded by the appearance of an increasing number of large Thy-1+, Lyt-1- blasts (days 2 and 4), the thymic cortex was repopulated (beginning on day 6) by smaller Thy-1+ cells which acquired Lyt-1, Lyt-2 and Lyt-3 though, obviously not in a strictly sequential manner. Simultaneously, the medullary radioresistant cells disappeared, nd the medulla was subsequently repopulated (beginning on day 8) by thymocytes of a mature phenotype. Early restitution of the thymus in radiation control mice was similar to the bone marrow chimeras. The results indicate that the histological restitution of the thymus originates substantially from radioresistant precursors of host origin. Graft-versus-host reaction induced by untreated allogeneic bone marrow cells prevented normal thymic restitution. A delayed localized cortical repopulation with small Thy-1+, Lyt-1+2+3+ cells, progressive destruction of thymic architecture and almost no restoration of the medullary immunocompetent thymocytes were noted. T cell differentiation obviously was seriously affected by the injuries to the thymic microenvironment due to alloreactive T cells.     

Antigen-presenting characteristics of peritoneal cells of Salmonella enteritidis 11RX-infected mice.

Investigation of the possibility that infection with intracellular bacterial parasites such as Salmonellae may modulate the function of antigen-presenting cells (APC) revealed no major change in APC function of peritoneal cells (PC) harvested from the peritoneal cavity of mice 1-3 days after intraperitoneal immunization with S. enteritidis 11RX. Analysis of the phenotype of the Salmonella-primed T cells which responded when cultured with PC from either normal or infected mice and Salmonella-antigen showed that only L3T4+ T cells proliferated. This was also true when PC from normal and infected mice were compared for their ability to induce allogeneic responses; both L3T4+ and Lyt-2.2+ T cells were induced to proliferate, with the majority belonging to the class I restricted, Lyt-2.2+ phenotype. Significant levels of alloantigen-specific Lyt-2.2+ cytotoxic T-cell activity were also induced in both types of cultures. However, a minor population of adherent cells which inhibited Salmonella antigen-specific T-cell proliferation in vitro was detected in peritoneal cell suspensions harvested 3 days after intraperitoneal immunization with S. enteritidis 11RX. Further characterization of these peritoneal cells revealed that they also inhibited the induction of in vitro T-cell responses to alloantigens. It is likely that the cells mediating these inhibitory effects belonged to a macrophage-like subset.     

L3T4 and Lyt-2 T cells are both involved in the generation of low-dose streptozotocin-induced diabetes in mice.

In order to determine the role of different T lymphocyte subsets in the pathogenesis of low-dose streptozotocin (LD-Sz) induced diabetes, we treated mice with Sz together with repeated injections of rat monoclonal antibodies (MoAb) with specificity towards the mouse T cell differentiation markers L3T4 ('helper/inducer' T cells and some macrophages), Lyt-2 ('cytotoxic/suppressor' T cells and NK cells) and Thy-1 (pan T lymphocytes). Treatment depleted target cells in peripheral blood and spleen; decreased the ability of spleen cells to respond to mitogens; and, in the case of depletion of the L3T4 T cell subset, prevented a humoral immune response to SRBC. Treatment with MoAb against either of the two T cell subtypes could protect from hyperglycaemia and loss of body weight, suggesting that both T cell subsets were implicated in the development of LD-Sz induced diabetes. Immunocytochemical analysis of pancreatic sections showed that both L3T4+ and Lyt-2+ cells participated in islet infiltration together with macrophages. Treatment with MoAb markedly reduced islet infiltration by both L3T4+ and Lyt-2+ cells but not by macrophages. The suppressive effect of MoAb against either L3T4 or Lyt-2 on diabetes development suggests that the pathomechanism involved is different from that in experimental autoimmune neuritis and adjuvant arthritis where Lyt-2 cells are not involved.     

Phenotypic analysis of splenic lymphocytes and immunohistochemical study of hepatic granulomas after a murine infection with Salmonella abortusovis.

Infection in mice with an attenuated strain of Salmonella abortusovis (SAO), a specific pathogen for sheep, was used as a convenient model to understand further the induced immunity against SAO. The hypovirulent Rv6 strain, subcutaneously inoculated in salmonella-susceptible BALB/cby (Itys) mice, colonized the spleen and the liver in less than 6 days post-infection (PI) to be cleared after Day 28 PI. Simultaneously, an increase in spleen cell numbers, splenomegaly and hepatic granulomatous lesions developed to a maximum level on Day 9 PI. In spleen of uninfected mice, the number of Thy-1.2+ cells represents twice the number of surface immunoglobulin-positive cells (sIg+). Cytofluorometric analysis of the spleen lymphoid cell subsets showed a significant increase (10 times, P less than 0.05) in the number of sIg+ cells from Day 6 to Day 28 PI compared to control values. The number of Thy-1.2+ cells also significantly increased, to a lesser degree than the sIg+ cells, on Day 2 and on Day 16 PI (twice control values, P less than 0.05), but decreased on Day 6 PI compared to Day 2 PI. The highest L3T4+:Lyt-2+ ratio was observed on Day 2 PI and the lowest on Day 9 PI. On Day 28 PI, the number of sIg+ cells was still greater than the number of Thy-1.2+ cells. The granulomatous lesions were observed in the liver as early as Day 2 PI and their frequency was maximal on Day 9 PI. Immunohistochemical analysis of the granulomatous lesions showed that macrophages (F4/80+, Mac1+) were the basic cells and that L3T4+ cells were the predominant T cells. In well-developed granulomas observed on Day 9 PI, macrophages were in the centre whereas L3T4+ T cells were preferentially located at the periphery. T cells expressing Lyt-2 antigen were rarely detected. Variations in the proportion of lymphoid cells in the spleen and in hepatic granulomatous lesions suggest different and complementary effector mechanisms in induced immunity against SAO.     

T-cell subsets in delayed-type hypersensitivity, protection, and granuloma formation in primary and secondary Listeria infection in mice: superior role of Lyt-2+ cells in acquired immunity.

Immunity to Listeria monocytogenes was studied in mice treated with rat monoclonal antibodies (MAbs) specific for the Thy-1.2, L3T4, and Lyt-2 T-cell markers. Three characteristic T-cell-mediated phenomena were investigated. Delayed-type hypersensitivity (DTH) to listerial antigen was totally abolished in mice treated with anti-Thy-1.2 or anti-L3T4 MAbs, whereas anti-Lyt-2 MAb treatment had no effect, regardless of whether the MAb was given during the induction or the expression of DTH. On the other hand, the elimination of bacteria from the spleens of infected animals was inhibited only by the application of either anti-Thy-1.2 MAb or anti-Lyt-2 MAb. This could be shown most impressively during the secondary infection of immune mice with a normally lethal dose of listeriae. In this situation, treatment with anti-Lyt-2 MAb sufficed to completely abolish immunologic memory, whereas anti-L3T4 MAb had only a marginal effect on antibacterial protection. However, the accelerated development of mononuclear cell foci in the livers of immune mice was inhibited by the application of both anti-L3T4 MAb and anti-Lyt-2 MAb. It is concluded that in murine listeriosis, DTH and acquired immunity to reinfection are dissociable phenomena. Although DTH is a function of L3T4+ T lymphocytes, Lyt-2+ T cells are necessary and sufficient for the expression of acquired resistance to L. monocytogenes. The roles of the different T-cell subsets in granuloma formation warrant further investigation.     

Con A response and interleukin 2 receptor expression of thymocytes rosetting with phagocytic cells of the thymic reticulum

Thymocytes bind to the phagocytic cells of the thymic reticulum (P-TR) and spontaneously forming rosettes were isolated and characterized. Rosetting thymocyte subsets included cells expressing different surface phenotype: most of them (91%) were of the double positive L3T4+ Lyt-2+ phenotype; a minor subpopulation (2.4%) expressed the helper L3T4+ Lyt-2- phenotype and finally a small subpopulation (6.3%) was negative for both L3T4 and Lyt-2 markers. Although the rosetting thymocytes were not enriched in mature single positive cells as compared to the non rosetting population, they showed a higher responsiveness to ConA plus recombinant IL-2. Moreover the rosetting thymocytes were induced to express IL-2 receptors just after stimulation with ConA whereas co-stimulation with ConA plus IL-2 was essential for the generation of IL-2 receptors on the non rosetting and total thymocytes. The possibility that the rosetting thymocytes acquired this activity during the rosetting process is discussed.