CD4+CD45RA+ and CD4+CD45RA- T cell subsets in man maintain distinct function and CD45RA expression persists on a subpopulation of CD45RA+ cells after activation with Con A.

We have previously shown that Con A-induced suppressor T cells belong to the CD45RA+ subset. After unseparated T cells are activated with Con A, CD45RA expression increases to a maximum (Day 2), and then decreases significantly, but does not disappear entirely (Day 9), while CD29 expression increases steadily. In the present study, we examined the fate of these cell surface molecules on isolated CD4+CD45RA+ and CD4+CD45RA- cells following activation with Con A, and their relationship to the regulatory functions of these subsets. After activation of CD4+CD45RA+ cells with Con A, CD45RO and CD29 antigen expression rapidly increases (greater than 90%). While CD45RA expression is downregulated, approximately 40% of the cells continue to express low-density CD45RA in a stable fashion through Day 21. Despite these phenotypic changes, cells originally CD45RA+ continue to suppress IgG synthesis and provide only minimal B cell help. Furthermore, when cells originally CD45RA+ were sorted on the basis of continued presence, or loss of CD45RA antigen 14 days after activation, both populations demonstrated potent suppression and minimal help. In contrast, after activation with Con A, CD4+CD45A- cells maintain stable phenotype and provide significant help and minimal suppression. Immunoprecipitation of the CD45RA antigen from Day 14 activated CD4+CD45RA+ cells confirms the continued presence of the 205-kDa isoform, but reveals a significant decrease in the 220-kDa isoform. These results suggest that after activation with Con A, cells originally CD45RA+ remain functionally distinct from cells originally CD45RA-, and that CD45RA antigen persists on a subpopulation of CD45RA+ cells after activation with Con A.     

Immunoregulatory T lymphocytes in man. Soluble antigen-specific suppressor-inducer T lymphocytes are derived from the CD4+CD45R-p80+ subpopulation

Regulation of the immune response in man is largely dependent on interactions between cells of the cluster designation 4+ (CD4+) helper/inducer sublineage and the CD8+ suppressor/cytotoxic sublineage. When cultured with autologous antigen-primed CD4+ lymphocytes, CD8+ cells differentiate into suppressor T cells (Ts) that specifically inhibit the response of fresh autologous CD4+ cells to the priming antigen only. The current study was undertaken to analyze the roles in this suppressor circuit of subpopulations of the CD4+ sublineage distinguished from one another on the basis of their binding (or lack of binding) to monoclonal antibodies against molecules p80 (Leu8) and CD45R (p220/Leu18/2H4). When examined for the proliferative responses to alloantigenic stimuli, each of the four: CD4+p80+, CD4+p80-, CD4+CD45R+, and CD4+CD45R- populations proliferated vigorously, synthesized interleukin 2 (IL-2) and interferon and released soluble IL-2 receptors. However, the responses to soluble antigens such as Candida and diphtheria toxoid were exhibited by CD4+CD45R-, CD4+p80+, and CD4+p80- cells, but not by CD4+CD45R+ cells. When examined for their ability to induced CD8+ Ts in the Candida-driven suppressor-induction culture system, only CD4+p80+ and CD4+CD45R- cells induced strong suppression. Further, when CD4+CD45R- cells were separated into CD4+CD45R-p80+ and CD4+CD45R-p80- subpopulations, despite the ability of both subpopulations to respond to Candida, only CD4+CD45R-p80+ cells induced autologous CD8+ Ts. Activated CD8+ Ts suppressed not only proliferation but also the release of soluble IL-2 receptors by autologous antigen-activated CD4+ cells. Thus, the antigen-specific suppressor-inducer T cells appear to be derived from the CD4+CD45R-p80+ (Leu3+, Leu8+, 2H4-) subpopulation of the CD4+ sublineage.     

Identification of a CD2- CD3+ T cell receptor-gamma+ peripheral blood lymphocyte subpopulation

We have identified, in a healthy individual, a sub-population of human peripheral lymphocytes which surface express a CD3-TCR-gamma complex recognized by anti-Ti gamma A mAb, while being unreactive with a phycoerythrin-conjugated anti-CD2 antibody with T11/1 specificity. Further immunofluorescence analyses performed on uncultured cells indicated that such a putative CD2-CD3+ phenotype was restricted to a fraction of those T lymphocytes which carry a surface receptor of the "second family" (gamma/delta). The actual lack of CD2 expression was confirmed by a subsequent series of cloning experiments which showed that none of the three well characterized CD2 epitopic clusters, namely T11/1, T11/2, and T11/3, were detectable on the surface of the relevant cells. The cultured CD2-, CD3+/TCR gamma + lymphocytes were found to display, as well as their CD2+ counterparts, both non-MHC-restricted cytotoxic function and proliferative responses induced via the gamma receptor complex. In contrast, the proliferative capacity of the CD2-, CD3+/TCR-gamma + cells observed in a culture system designed for in vitro expansion of lymphocytes with undefined specificity was extremely limited. This may relate to an impaired interaction of the CD2- cloned lymphocytes with lymphocyte function-associated (LFA)3+ irradiated cells present in the feeder layer. Further characterization of such minor CD2- T lymphocytes subsets may help to better understand the biologic relevance of the CD2/LFA3 pathway of cell-cell interaction.     

Reversible senescence in human CD4+CD45RA+CD27- memory T cells

Persistent viral infections and inflammatory syndromes induce the accumulation of T cells with characteristics of terminal differentiation or senescence. However, the mechanism that regulates the end-stage differentiation of these cells is unclear. Human CD4(+) effector memory (EM) T cells (CD27(-)CD45RA(-)) and also EM T cells that re-express CD45RA (CD27(-)CD45RA(+); EMRA) have many characteristics of end-stage differentiation. These include the expression of surface KLRG1 and CD57, reduced replicative capacity, decreased survival, and high expression of nuclear γH2AX after TCR activation. A paradoxical observation was that although CD4(+) EMRA T cells exhibit defective telomerase activity after activation, they have significantly longer telomeres than central memory (CM)-like (CD27(+)CD45RA(-)) and EM (CD27(-)CD45RA(-)) CD4(+) T cells. This suggested that telomerase activity was actively inhibited in this population. Because proinflammatory cytokines such as TNF-α inhibited telomerase activity in T cells via a p38 MAPK pathway, we investigated the involvement of p38 signaling in CD4(+) EMRA T cells. We found that the expression of both total and phosphorylated p38 was highest in the EM and EMRA compared with that of other CD4(+) T cell subsets. Furthermore, the inhibition of p38 signaling, especially in CD4(+) EMRA T cells, significantly enhanced their telomerase activity and survival after TCR activation. Thus, activation of the p38 MAPK pathway is directly involved in certain senescence characteristics of highly differentiated CD4(+) T cells. In particular, CD4(+) EMRA T cells have features of telomere-independent senescence that are regulated by active cell signaling pathways that are reversible.     

Human CD8+ T lymphocytes can be divided into CD45RA+ and CD45RO+ cells with different requirements for activation and differentiation.

The functional distinction between CD45RA+ and CD45RO+ cells within the human CD4+ T cell subset is well established. This study was undertaken to investigate whether a similar division can be made within the CD8+ T cell population. A quantitative comparison was made of the requirements for activation and differentiation of CD8+CD45RA+ and CD8+CD45RO+ cells. Stimulation of T lymphocytes with anti-CD3 mAb immobilized at high-density induced strong proliferation and CTL activity in both CD45RA+ and CD45RO+ cells. Suboptimal TCR/CD3 triggering, in contrast, induced substantially higher levels of proliferation and CTL activity in CD8+CD45RO+ cells compared with their CD45RA+ counterparts. Lymphokine secretion (i.e., Il-2 and TNF-alpha) was under any condition more readily induced in CD8+CD45RO+ cells. Markedly, proliferation of both CD8+CD45RA+ and CD8+CD45RO+ T cells initiated by anti-CD3 mAb immobilized at high densities was not inhibited by addition of anti-CD25 mAb, in contrast to proliferation induced by suboptimal anti-CD3 mAb concentrations. These findings show that a functional division between CD45RA+ and CD45RO+ T cells with distinct requirements for activation and differentiation may also be made in the CD8+ subset.     

Differential in vitro activation of CD8-CD4+ and CD4-CD8+ T lymphocytes by combinations of anti-CD2 and anti-CD3 antibodies

Purified peripheral blood T lymphocytes and the CD8-CD4+ and CD4-CD8+ T cell subsets, exhaustively depleted of APC have been studied for their capacity to respond to mAb directed against the CD3-Ti Ag-specific TCR complex and against the CD2 SRBCR. It is demonstrated that high affinity IL-2R can be readily induced by either anti-CD3 and/or anti-CD2 stimulation. However, IL-2 production can be observed only in the CD4+CD8- T cell subset. These results clearly contrast data obtained with purified CD4-CD8+ T cells, which are able to proliferate when the CD3-Ti complex is activated in the presence of APC. The data presented in the present study demonstrate that a simplified model for T cell activation and clonal expansion of the two major T cell subsets involve only the CD3-Ti complex and the CD2 Ag. Under conditions where the activation signals for the T cells are restricted only to the activation of CD3-Ti and CD2, the CD4+CD8- T cells respond with IL-2 production and expression of high affinity IL-2R, whereas the CD4-CD8+ T cell subset depends on exogenous IL-2 provided by the CD4+CD8- cells. These data do not, however, exclude an involvement of other cell-surface signals for regulation and control of T cell activation and T cell effector functions.     

Differential interleukin secretion by in vitro activated human CD45RA and CD45RO CD4+ T cell subsets.

The CD45RA and CD45RO isoforms have been reported to define complementary subsets among CD4+ T cells: CD45RA CD4+ T cells are considered "virgin T cells" and CD45RO "primed T cells." We investigated the secretion of lymphokines by human CD4+ CD45RO and CD4+ CD45RA T helper cells after mitogen stimulation. CD45RA and CD45RO CD4+ T cells were isolated by negative immunoselection using magnetic beads. CD45RO cells, but not CD45RA cells, proliferate well in response to pokeweed mitogen (PWM) or insoluble anti-CD3. Both subpopulations produced interleukin (IL)-2, IL-6, and interferon (IFN)-gamma when stimulated with PWM for 1-4 days. Only Day 1 supernatants from CD45RO cells contained moderate amounts of IL-4. After 14 days of continuous culture and stimulation with PWM, the CD45RA subset had lost the expression of CD45RA and gained that of CD45RO. When long-term cultured CD45RA or CD45RO cells were treated with insoluble anti-CD3, they incorporated [3H]thymidine at similar levels, but only CD45RO cells secreted IL-4 and significantly increased their secretion of IFN-gamma. These data indicate that despite phenotype conversion, the two subpopulations maintain functional differences in the secretion of lymphokines, thus suggesting that circulating CD45RA and CD45RO cells may represent different lines of differentiation.     

Differential responses of CD4+CD45RA+ and CD4+CD29+ subsets to activated CD8+ cells: enhanced stimulation of the CD4+CD45RA+ subset by cells from patients with multiple sclerosis.

To examine whether functionally different CD4+ cells respond uniformly to the immunoregulatory influences of allogeneic activated CD8+ cells (*CD8+), we subfractionated the CD4+ population into two subsets, based on the high expression of either CD45RA or CD29. We confirmed that the CD45RA+ cells proliferated poorly in response to soluble anti-CD3 mAb, compared to the vigorous response obtained with the CD29+ subset; the CD45RA+ cells were more responsive to stimulation with Con A. Using normal healthy controls, we found that whereas *CD8+ had a significant suppressive effect on the proliferation of the CD29+ subset, they augmented the mitogen-induced proliferative response of the CD45RA+ cells. We further demonstrated that *CD8+ derived from MS patients augmented the response of the CD45RA+ subset to a significantly higher degree compared to healthy age- and sex-matched controls. There were no significant differences between the degree of suppression exerted by the *CD8+ of either the MS or the control group on the CD29+ cells. These results demonstrate that helper/memory CD4+CD29+ cells are more sensitive to the suppressive influences of *CD8+ compared to the CD4+CD45RA+ subset. In addition, in MS, *CD8+ may contribute to a more pronounced "on" signal for virgin CD4+CD45RA+ cells, which might serve as a means to perpetuate the autoimmune disease process.     

Frequencies of circulating cytolytic,CD45RA+CD27-, CD8+ T lymphocytes depend on infection with CMV

Viral infections may cause serious disease unless the adaptive immune system is able to clear the viral agents through its effector arms. Recent identification and functional characterization of subpopulations of human CD8(+) T cells has set the stage to study the correlation between the appearance of particular subsets and common viral infections during childhood, i.e., EBV, CMV, varicella-zoster virus (VZV), and the attenuated measles-mumps-rubella (MMR) vaccine strains. In a cohort of 220 healthy children we analyzed lymphocytes and subpopulations of CD4(+) and CD8(+) T cells. The presence of the cytolytic CD45RA(+)CD27(-) subset of CD8(+) T cells correlated with prior CMV infection as defined by seroconversion (p < 0.0001). The number of this CD8(+) T cell subset remained stable during follow-up over 3 years in 40 children. The CD45RA(+)CD27(-) subset of CD8(+) T cells first appeared during acute CMV infection and subsequently stabilized at an individual set-point defined by age and immunocompetence. The functional importance of these cells in CMV surveillance was reflected by their increased numbers in immunosuppressed pediatric kidney transplant patients. Preferential expansion of CD8(+)CD45RA(+)CD27(-) cytolytic T cells seems unique for CMV.     

Recirculatory and sessile CD4+ T lymphocytes differ on CD45RC expression

CD4+ T cell subsets are unequally distributed in rat secondary lymphoid organs. Those with the memory phenotype CD45RClow Thy-1- L-selectin- are present at a higher frequency in Peyer's patches (PP) than in lymph nodes and spleen, and increase in numbers with age in all three tissues, particularly in the PP. Homing experiments revealed that CD4+ T cells that recirculate through secondary lymphoid organs are mainly CD45RChigh. It was also apparent that the ability of recirculating cells to enter different lymphoid organs varies; less cells enter PP than the spleen or lymph nodes. Our results also reveal the existence of a nonrecirculating population of CD4+ T cells in secondary lymphoid organs, which are predominantly, if not exclusively, CD45RClow. Our results show that secondary lymphoid organs differ in their CD4+ T cell subset composition as a consequence of having different ratios of recirculatory:nonrecirculatory CD4+ T cells, and these cells display a different CD45RC phenotype.     

The functional heterogeneity of CD8+ cells defined by anti-CD45RA (2H4) and anti-CD29 (4B4) antibodies.

The monoclonal antibodies, anti-2H4(CD45RA), and anti-4B4(CD29), along with UCHL1-(CD45RO), identify reciprocal populations of CD4 cells with distinct suppressor inducer (CD45RA+CD29-CD45RO-) and helper inducer (CD45RA-CD29+CD45RO+) functions. Although the CD8+ population is known to contain precytotoxic, cytotoxic, suppressor, and some natural killer cells, the exact phenotypic identities of these functional CD8 subsets has not been established. In this study, we tried to determine whether these monoclonal antibodies could distinguish functionally distinct subsets of cells within the CD8+ population. For this purpose, whole T cells or fractionated T cells were sensitized with irradiated allogeneic non-T cells for 6 days, following which, CD8+ or CD8+CD11b- cells were isolated and cellular functions such as suppressor, killer precursor, and killer effector activity were assessed. The results showed that both class I-restricted alloantigen-specific killer effector and killer precursor cells belonged to the CD8+CD11b-CD45RA-CD29+ population. Moreover, these killer effector cells expressed the CTL-associated S6F1 molecule, an epitope of the LFA-1 antigen. In contrast, suppressor effector cells belonged to the CD8+CD11b-CD45RA+CD29- cell population. Although the UCHL1 antigen has been reported to define the CD4+CD29+ helper inducer cell, over 90% of allo-activated CD8+ cells expressed this antigen, whereas only 40-60% of these cells expressed either CD45RA or CD29 antigens. These results suggest that anti-CD45RA and anti-CD29 antibodies may provide useful tools for distinguishing between suppressor effector versus killer effector and killer precursor cells within the CD8+CD11b- population.     

Stimulation via the CD3 and CD28 molecules induces responsiveness to IL-4 in CD4+CD29+CD45R- memory T lymphocytes

Although both IL-2 and IL-4 can promote the growth of activated T cells, IL-4 appears to selectively promote the growth of those helper/inducer and cytolytic T cells which have been activated via their CD3/TCR complex. The present study examines the participation of CD28 and certain other T cell-surface molecules in inducing T cell responsiveness to IL-4. Purified small high density T cells were cultured in the absence of accessory cells with various soluble anti-human T cell mAb with or without soluble anti-CD3 mAb and their responsiveness to IL-4 was studied. None of the soluble anti-T cell mAb alone was able to induce T cell proliferation in response to IL-4. A combination of soluble anti-CD3 with anti-CD28 mAb but not with mAb directed at the CD2, CD5, CD7, CD11a/CD18, or class I MHC molecules induced T cell proliferation in response to IL-4. Anti-CD2 and anti-CD5 mAb enhanced and anti-CD18 mAb inhibited this anti-CD3 + anti-CD28 mAb-induced T cell response to IL-4. In addition, anti-CD2 in combination with anti-CD3 and anti-CD28 mAb induced modest levels of T cell proliferation even in the absence of exogenous cytokines. IL-1, IL-6, and TNF were each unable to replace either anti-CD3 or anti-CD28 mAb in the induction of T cell responsiveness to IL-4, but both IL-1 and TNF enhanced this response. The anti-CD3 + anti-CD28 mAb-induced response to IL-4 was exhibited only by cells within the CD4+CD29+CD45R- memory T subpopulation, and not by CD8+ or CD4+CD45R+ naive T cells. When individually cross-linked with goat anti-mouse IgG antibody immobilized on plastic surface, only anti-CD3 and anti-CD28 mAb were able to induce T cell proliferation. These results indicate that the CD3 and CD28 molecules play a crucial role in inducing T cell responsiveness to IL-4 and that the CD2, CD5, and CD11a/CD18 molecules influence this process.     

Decreased effector memory CD45RA+ CD62L- CD8+ T cells and increased central memory CD45RA- CD62L+ CD8+ T cells in peripheral blood of rheumatoid arthritis patients

Although a role for CD8+ T cells in the pathogenesis of rheumatoid arthritis (RA) has been suggested, the precise nature of their involvement is not fully understood. In the present study we examined the central and effector memory phenotypes of CD4+ and CD8+ T cells in the peripheral blood of patients with RA and systemic lupus erythematosus. Terminally differentiated effector memory CD45RA+CD62L-CD8+ T cells were significantly decreased in RA patients, whereas the central memory CD45RA-CD62L+ CD8+ T-cell population was increased as compared with levels in healthy control individuals. Na?ve and preterminally differentiated effector memory CD45RA-CD62L- CD8+ T cells did not differ between RA patients and control individuals. The CD45RA-CD62L+ central memory CD4+ T-cell subpopulation was increased in RA patients, whereas the na?ve and effector memory phenotype of CD4+ T cells did not differ between RA patients and control individuals. In patients with systemic lupus erythematosus the distribution of na?ve/memory CD4+ and CD8+ T cells did not differ from that in age- and sex-matched control individuals. These findings show that peripheral blood CD8+ T cells from RA patients exhibit a skewed maturation phenotype that suggests a perturbation in the homeostasis of these cells. The central memory CD45RA-CD62L+ CD4+ and CD8+ T-cell numbers were increased in RA, suggesting an accelerated maturation of na?ve T cells. The decreased numbers of terminally differentiated CD45RA+CD62L- effector memory CD8+ T cells in peripheral blood of RA patients may reflect increased apoptosis of these cells or enhanced migration of these cells to sites of inflammation, which may play a role in the pathogenesis of RA.     

Functional maturation of CD4+CD25+CTLA4+CD45RA+ T regulatory cells in human neonatal T cell responses to environmental antigens/allergens

A number of laboratories have reported cord blood T cell responses to ubiquitous environmental Ags, including allergens, by proliferation and cytokine secretion. Moreover, the magnitude of these responses has been linked with risk for subsequent expression of allergy. These findings have been widely interpreted as evidence for transplacental priming and the development of fetal T memory cells against Ags present in the maternal environment. However, we present findings below that suggest that neonatal T cell responses to allergens (and other Ags) differ markedly from those occurring in later life. Notably, in contrast to allergen-responsive adult CD4(+) T cell cultures, responding neonatal T cell cultures display high levels of apoptosis. Comparable responses were observed against a range of microbial Ags and against a parasite Ag absent from the local environment, but not against autoantigen. A notable finding was the appearance in these cultures of CD4(+)CD25(+)CTLA4(+) T cells that de novo develop MLR-suppressive activity. These cells moreover expressed CD45RA and CD38, hallmarks of recent thymic emigrants. CFSE-labeling studies indicate that the CD4(+)CD25(+) cells observed at the end of the culture period were present in the day 0 starting populations, but they were not suppressive in MLR responses. Collectively, these findings suggest that a significant component of the reactivity of human neonatal CD4(+) T cells toward nominal Ag (allergen) represents a default response by recent thymic emigrants, providing an initial burst of short-lived cellular immunity in the absence of conventional T cell memory, which is limited in intensity and duration via the parallel activation of regulatory T cells.     

Rapid response to Con A by CD4+CD45R- rat memory lymphocytes as compared to CD4+CD45R+ lymphocytes

Functionally distinct subpopulations within the CD4+ subset of T lymphocytes have been described in man, rat, and mouse. In the rat different functions have been assigned to CD45R+ and CD45R- T helper cells. The CD45R+ in contrast to the CD45R- T helper cells have been reported to produce IL-2 and to proliferate well in response both to Con A and in MLR. In the present investigation the kinetics of the response to Con A by the CD45R+ and CD45R- rat T helper subsets have been analyzed. We confirm a strong proliferative response to Con A by CD4+CD45R+ rat T lymphocytes and also that they are the best IL-2 producers. We further demonstrate that CD4+CD45R- cells also produce IL-2, although in order to appreciate this production quantitatively by assays of the culture supernatants it was necessary to block IL-2 absorption by IL-2 receptor (IL-2R) antibodies. This blockage was of importance also in comparisons of the two subsets, since they showed different kinetics of IL-2R appearance. It is demonstrated that the CD4+CD45R- cells respond more rapidly to Con A than the CD4+CD45R+ cells as reflected by phenotypic conversion, IL-2 production, and proliferation. The fast response of the CD4+CD45R- T subset shown in the present study of rat cells and analogous studies of human cells suggests that the memory compartment of T cells besides other characteristics also has the capacity for a more rapid response than naive lymphocytes.     

Infection of the CD45RA+ (naive) subset of peripheral CD8+ lymphocytes by human immunodeficiency virus type 1 in vivo

To investigate the mechanism and functional significance of infection of CD8+ lymphocytes by human immunodeficiency virus type 1 (HIV-1) in vivo, we determined frequencies of infection, proviral conformation, and genetic relationships between HIV-1 variants infecting naive (CD45RA+) and memory (CD45RO+) peripheral blood CD4+ and CD8+ lymphocytes. Infection of CD3+ CD8+ CD45RA+ cells was detected in 9 of 16 study subjects at frequencies ranging from 30 to 1,400 proviral copies/10(6) cells, more frequently than CD3+ CD8+ lymphocytes expressing the RO isoform of CD45 (n = 2, 70 and 260 copies /10(6) cells). In agreement with previous studies, there was no evidence for a similar preferential infection of CD4+ naive lymphocytes. Proviral sequences in both CD4+ and CD8+ lymphocyte subsets were complete, as assessed by quantitation using primers from the long terminal repeat region spanning the tRNA primer binding site. In six of the seven study subjects investigated, variants infecting CD8+ lymphocytes were partially or completely genetically distinct in the V3 region from those recovered from CD4+ lymphocytes and showed a greater degree of compartmentalization than observed between naive and memory subsets of CD4+ lymphocytes. In two study subjects, arginine substitutions at position 306, associated with use of the chemokine coreceptor CXCR4, were preferentially found in CD4 lymphocytes. These population differences may have originated through different times of infection rather than necessarily indicating a difference in their biological properties. The preferential distribution of HIV-1 in naive CD8+ lymphocytes indeed suggests that infection occurred early in T-lymphocyte ontogeny, such as during maturation in the thymus. Destruction of cells destined to become CD8+ lymphocytes may be a major factor in the decline in CD8+ lymphocyte frequencies and function on disease progression and may contribute directly to the observed immunodeficiency in AIDS.     

Rat peripheral CD4+CD8+ T lymphocytes are partially immunocompetent thymus-derived cells that undergo post-thymic maturation to become functionally mature CD4+ T lymphocytes

CD4+CD8+ double-positive (DP) T cells represent a minor subpopulation of T lymphocytes found in the periphery of adult rats. In this study, we show that peripheral DP T cells appear among the first T cells that colonize the peripheral lymphoid organs during fetal life, and represent approximately 40% of peripheral T cells during the perinatal period. Later their proportion decreases to reach the low values seen in adulthood. Most DP T cells are small size lymphocytes that do not exhibit an activated phenotype, and their proliferative rate is similar to that of the other peripheral T cell subpopulations. Only 30-40% of DP T cells expresses CD8beta chain, the remaining cells expressing CD8alphaalpha homodimers. However, both DP T cell subsets have an intrathymic origin since they appear in the recent thymic emigrant population after injection of FITC intrathymically. Functionally, although DP T cells are resistant to undergo apoptosis in response to glucocorticoids, they show poor proliferative responses upon CD3/TCR stimulation due to their inability to produce IL-2. A fraction of DP T cells are not actively synthesizing the CD8 coreceptor, and they gradually differentiate to the CD4 cell lineage in reaggregation cultures. Transfer of DP T lymphocytes into thymectomized SCID mice demonstrates that these cells undergo post-thymic maturation in the peripheral lymphoid organs and that their CD4 cell progeny is fully immunocompetent, as judged by its ability to survive and expand in peripheral lymphoid organs, to proliferate in response to CD3 ligation, and to produce IL-2 upon stimulation.     

In vivo ultraviolet-exposed human epidermal cells activate T suppressor cell pathways that involve CD4+CD45RA+ suppressor-inducer T cells

In vivo UV exposure of human epidermis abrogates the function of CD1+DR+ Langerhans cells and induces the appearance of CD1-DR+ Ag-presenting macrophages. Epidermal cells from UV-exposed skin, in contrast to epidermal cells from normal skin, potently activate autologous CD4+ T cells, and, in particular, the CD45RA+ (2H4+) (suppressor-inducer) subset. We therefore determined whether UV-exposure in humans leads to a T cell response in which suppression dominates. Autologous blood T cells were incubated with epidermal cell suspensions from in vivo UV-irradiated skin. After activation, repurified T cells were transferred in graded numbers to autologous mononuclear cells (MNC) stimulated with PWM and the resultant IgG production analyzed by ELISA. Relative to T cells activated by unirradiated control epidermal cells, T cells activated by UV-exposed epidermal cells demonstrated enhanced capacity to suppress IgG production (n = 6; p less than or equal to 0.03). Within the T cell population, CD8+ cells stimulated by UV-exposed epidermal cells could be directly activated to suppress PWM-stimulated MNC Ig production if IL-2 was provided in the reaction mixture. The suppressive activity was also transferable with purified CD4+ T cells stimulated by UV-exposed epidermal cells (n = 10; p less than or equal to 0.01), and was radiosensitive. Suppression was decreased when PWM-stimulated MNC were depleted of CD8+ T cells before mixing with CD4+ T cells activated by UV-exposed epidermal cells, suggesting indirect induction of CD8+ Ts cells contained within the responding MNC populations. Indeed, physical depletion of CD45RA+ cells resulted in total abrogation of the suppressor function contained in the CD4+ T cells. Activation of suppressor function was critically dependent on DR+ APC contained in UV-exposed epidermis. The data suggest that UV-exposure modulates cutaneous APC activity in humans, as in mice, such that the dominant immune response is tilted toward suppression. These mechanisms in normal individuals may function to dampen responses to UV-induced endogenous Ag that are pathogenic in autoimmune disorders. However, these mechanisms might also facilitate the growth of UV-induced skin cancers.     

Immunophenotypic Characterization of CD45RO+ and CD45RA+ T Cell Subsets in Peripheral Blood of Peripheral T Cell Lymphoma Patients

To study the distribution profile of CD45RO⁺ and CD45RA⁺ T cells in the peripheral blood of peripheral T cell lymphoma (PTCL) patients and its clinical significance. 27 patients with PTCL were enrolled in this study, together with 30 healthy individuals as the control group. Flow cytometry analysis was employed to examinate the differences in the distribution of CD45RO⁺ and CD45RA⁺ T cells in peripheral blood between two groups. In PTCL patient’s lymphnode tissues, the T cell population displayed diverse antigenic expression, with CD4⁺ T cells as the major subset. No B cell-related antigen was expressed. The percentage of CD4⁺/CD8⁺ and CD4⁺CD45RO⁺ T cells in patients’ peripheral blood were significantly lower than that in the control samples, while the percentage of CD4⁺CD45RA⁺, CD8⁺CD45RA⁺, and CD8⁺CD45RO⁺ T cells in patients’ peripheral blood were significantly higher than that in the control samples. The percentage of CD4⁺/CD8⁺, CD4⁺CD45RO⁺ cells in stage I/II PTCL patients’ peripheral blood were significantly higher than that in the samples from patients with stage III/IV PTCL. The percentage of CD4⁺CD45RA⁺, CD8⁺CD45RA⁺, and CD8⁺CD45RO⁺ T cells were notably lower than that in the samples from III/IV period PTCL patients. Both CD45RO⁺ and CD45RA⁺ T cells play important roles in the process of PTCL. The immunophenotypic profile from this study will help to develop the differential diagnosis and treatment of PTCL patients in the future, and improve the accuracy rate of diagnosis and to ameliorate the prognosis.     

Human autoreactive CD4+ T cells from naive CD45RA+ and memory CD45RO+ subsets differ with respect to epitope specificity and functional antigen avidity

T cells with specificity for self-Ags are normally present in the peripheral blood, and, upon activation, may target tissue Ags and become involved in the pathogenesis of autoimmune processes. In multiple sclerosis, a demyelinating disease of the CNS, it is postulated that inflammatory damage is initiated by CD4+ T cells reactive to myelin Ags. To investigate the potential naive vs memory origin of circulating myelin-reactive cells, we have generated myelin basic protein (MBP)- and tetanus toxoid-specific T cell clones from CD45RA+/RO- and CD45RO+/RA- CD4+ T cell subsets from the peripheral blood of multiple sclerosis patients and controls. Our results show that 1) the response to MBP, different from that to TT, predominantly emerges from the CD45RA+ subset; 2) the reactivity to immunodominant MBP epitopes mostly resides in the CD45RA+ subset; 3) in each individual, the recognition of single MBP epitopes is skewed to either subset, with no overlap in the Ag fine specificity; and 4) in spite of a lower expression of costimulatory and adhesion molecules, CD45RA+ subset-derived clones recognize epitopes with higher functional Ag avidity. These findings point to a central role of the naive CD45RA+ T cell subset as the source for immunodominant, potentially pathogenic effector CD4+ T cell responses in humans.