CD45RA CD62L Research Articles

Immunologic, Virologic, and Neuropsychologic Responses in Human Immunodeficiency Virus-Infected Children Receiving Their First Highly Active Antiretroviral Therapy Regimen

Our objective was to measure the early dynamics, evolution, and durability over 96 wk of immunologic responses in children receiving their first highly active antiretroviral therapy (HAART) regimen. The study was designed as a prospective, single-arm study. Twelve human immunodeficiency virus (HIV)-infected children (median age, 11.8 yr) were enrolled. All subjects received stavudine, nevirapine, and ritonavir. Serial measurements included HIV viral load, lymphocyte subsets, thymic volume by computed tomography (CT), neurocognitive testing, and brain CT. Baseline median CD4(+) T cell count was 589 cells/mm(3) , viral load was 3.9 log(10) HIV RNA copies/mL, and thymic volume was 16.3 cm(3) . Ten children had an undetectable viral load at week 48. Eight maintained an undetectable viral load at 96 wk. The median increase in absolute CD4(+) T cell count was 225 cells/mm(3) by week 48, and 307 cells/mm(3) by week 96. The median increase in naive (CD45RA(+) CD62L(+) ) CD4(+) T cells was 133 cells/mm(3) by week 48, and 147 cells/mm(3) by week 96. The median number of naive CD8(+) T cells increased from 205 to 284 cells/mm(3) by week 24; this increase was sustained to week 96. The number of B cells increased and was associated with a decrease in immunoglobulin levels. The number of natural killer cells was stable. There were no significant changes in thymic volume. Most children exhibited stable cognitive function over the course of the study. We conclude that, in this cohort of relatively immunocompetent HIV-infected children, an initial HAART regimen was associated with rapid and sustained increases in total CD4(+) T cells, in naive CD4(+) and CD8(+) T cells, and in B cells through 96 wk.

Clinical outcomes and immune reconstitution in 103 advanced AIDS patients undergoing 12-month highly active antiretroviral therapy

Highly active antiretroviral therapy (HAART) produces profound suppression of HIV replication, substantial increase in CD4(+) T cells, and partial reconstitution of the immune system. However, the numbers of subjects were small in previous Chinese studies. This study evaluated the efficacy and side effects of HAART in Chinese advanced AIDS patients. One hundred and three antiretroviral drug naive AIDS patients were enrolled in this study and were divided into two groups by their baseline CD4(+) count: < 100 cells/microl or > or = 100 cells/microl. Clinical, virological and immunological outcomes were monitored at baseline and at 1, 3, 6, 9 and 12 months during the course of treatment with HAART. One patient died and another was lost from the follow-up. For the remaining 101 HIV/AIDS patients at the 12th month during the HAART, the plasma viral load (VL) was reduced to (3.2 +/- 0.7) lg copies/ml, the CD4(+) count increased to (168 +/- 51) cells/microl [among which the naive phenotype (CD45RA(+)CD62L(+)) increased to (49 +/- 27) cells/microl and the memory phenotype (CD45RA(-)) increased to (119 +/- 55) cells/microl], and the percentage of CD4(+)CD28(+) cells increased. At the same time, there was a significant reduction of CD8(+) T cell activation. In the 69 patients with the baseline CD4(+) count < 100 cells/microl, 37 had a VL < 50 copies/ml; while in the 34 patients with the baseline CD4(+) count > or = 100 cells/microl, 25 had a VL < 50 copies/ml, the difference between the two groups was statistically significant. The CD4(+) T cell count showed a two-phase increase during HAART and a significant positive correlation was shown between the change of CD4(+) count and plasma VL. Over 12 months of HAART, 10 patients had gastrointestinal side effects, 13 peripheral neuritis, 7 hepatic lesions, 8 hematological side effects, 8 skin rashes, 10 lipodystrophy and 1 renal calculus. Immune reconstitution as well as the significantly improved clinical outcomes is observed in Chinese advanced AIDS patients after HAART. Side effects are common during HAART and require clinical attention.

Age-dependent incidence, time course, and consequences of thymic renewal in adults

Homeostatic regulation of T cells involves an ongoing balance of new T cell generation, peripheral expansion, and turnover. The recovery of T cells when this balance is disrupted provides insight into the mechanisms that govern homeostasis. In a long-term, single cohort study, we assessed the role of thymic function after autologous transplant in adults, correlating serial computed tomography imaging of thymic size with concurrent measurements of peripheral CD4(+) T cell populations. We established the age-dependent incidence, time course, and duration of thymic enlargement in adults and demonstrated that these changes were correlated with peripheral recovery of naive CD45RA(+)CD62L(+) and signal-joint TCR rearrangement excision circle-bearing CD4(+) populations with broad TCR diversity. Furthermore, we demonstrated that renewed thymopoiesis was critical for the restoration of peripheral CD4(+) T cell populations. This recovery encompassed the recovery of normal CD4(+) T cell numbers, a low ratio of effector to central memory cells, and a broad repertoire of TCR Vbeta diversity among these memory cells. These data define the timeline and consequences of renewal of adult thymopoietic activity at levels able to quantitatively restore peripheral T cell populations. They further suggest that structural thymic regrowth serves as a basis for the regeneration of peripheral T cell populations.

Low‐Level Viremia and Proviral DNA Impede Immune Reconstitution in HIV‐1–Infected Patients Receiving Highly Active Antiretroviral Therapy

Immunological and virological consequences of low-level viremia in human immunodeficiency virus (HIV) type 1-infected patients receiving highly active antiretroviral therapy (HAART) remain to be determined. For 24 months, 101 HAART-treated, HIV-1-infected patients with HIV RNA levels </=200 copies/mL were followed prospectively: HIV RNA level and CD4 and CD8 cell counts were investigated every 3 months, and proviral DNA and T cell subsets were investigated every 6 months. During follow-up, 33 patients had HIV RNA levels </=20 copies/mL at all visits (uVL patients), whereas 68 patients had HIV RNA levels >20 copies/mL at >/=1 visit (dVL patients) (median increase, 81 copies/mL [interquartile range, 37-480 copies/mL]). dVL patients had higher concentrations of CD8 cells, activated and memory T cells, and proviral DNA, compared with uVL patients (P<.05). A higher HIV RNA level was independently associated with reduced CD4 gain (P<.001). A higher HIV RNA level also was associated with increases in activated CD8(+)CD38(+) and CD8(+)HLA-DR(+) cells (P<.05), and a higher level of activated CD8(+)CD38(+) cells was independently associated with reduced CD4 gain (P<.05). A higher proviral DNA level was associated with increases in CD4(+)CD45RA(-)CD28(-) effector cells and reductions in naive CD4(+)CD45RA(+)CD62L(+) and CD8(+)CD45RA(+)CD62L(+) cells (P<.05). Higher levels of activated CD4(+)HLA-DR(+) and early differentiated CD4(+)CD45RA(-)CD28(+) cells predicted increased risk of subsequent detectable viremia in patients with undetectable HIV RNA (P<.05). These findings indicate that low-level viremia and proviral DNA are intimately associated with the immunological and virological equilibrium in patients receiving HAART.

Specifically activated memory T cell subsets from cancer patients recognize and reject xenotransplanted autologous tumors

Bone marrow of breast cancer patients was found to contain CD8+ T cells specific for peptides derived from breast cancer–associated proteins MUC1 and Her-2/neu. Most of these cells had a central or effector memory phenotype (CD45RA–CD62L+ or CD45RA–CD62L–, respectively). To test their in vivo function, we separated bone marrow–derived CD45RA+ naive or CD45RA–CD45RO+ memory T cells, stimulated them with autologous dendritic cells pulsed with tumor lysate, and transferred them into NOD/SCID mice bearing autologous breast tumors and normal skin transplants. CD45RA– memory but not CD45RA+ naive T cells infiltrated autologous tumor but not skin tissues after the transfer. These tumor-infiltrating cells had a central or effector memory phenotype and produced perforin. Many of them expressed the P-selectin glycoprotein ligand 1 and were found around P-selectin+ tumor endothelium. Tumor infiltration included cluster formation in tumor tissue by memory T cells with cotransferred dendritic cells. It was associated with the induction of tumor cell apoptosis and significant tumor reduction. We thus demonstrate selective homing of memory T cells to human tumors and suggest that tumor rejection is based on the recognition of tumor-associated antigens on tumor cells and dendritic cells by autologous specifically activated central and effector memory T cells.

Specifically activated memory T cell subsets from cancer patients recognize and reject xenotransplanted autologous tumors.

Bone marrow of breast cancer patients was found to contain CD8(+) T cells specific for peptides derived from breast cancer-associated proteins MUC1 and Her-2/neu. Most of these cells had a central or effector memory phenotype (CD45RA(-)CD62L(+) or CD45RA(-)CD62L(-), respectively). To test their in vivo function, we separated bone marrow-derived CD45RA(+) naive or CD45RA(-)CD45RO(+) memory T cells, stimulated them with autologous dendritic cells pulsed with tumor lysate, and transferred them into NOD/SCID mice bearing autologous breast tumors and normal skin transplants. CD45RA(-) memory but not CD45RA(+) naive T cells infiltrated autologous tumor but not skin tissues after the transfer. These tumor-infiltrating cells had a central or effector memory phenotype and produced perforin. Many of them expressed the P-selectin glycoprotein ligand 1 and were found around P-selectin(+) tumor endothelium. Tumor infiltration included cluster formation in tumor tissue by memory T cells with cotransferred dendritic cells. It was associated with the induction of tumor cell apoptosis and significant tumor reduction. We thus demonstrate selective homing of memory T cells to human tumors and suggest that tumor rejection is based on the recognition of tumor-associated antigens on tumor cells and dendritic cells by autologous specifically activated central and effector memory T cells.

Decrease in Fine T‐cell Subset ratio MT2/MT1 During Steroid Reduction of Asthmatic Patients

Combining inhaled long‐acting β‐2 agonist (LABA) and inhaled corticosteroid (ICS) seems to offer asthma control at a lower dose of ICS than achieved by ICS alone. Fine mapping of T‐cell surface markers by flow cytometry offers a detailed status of the individual's inflammatory response. The frequency of MT2 (CD4+CD45RA–CD62L+CD11adim) and MT1 (CD4+CD45RA–CD62L–CD11abright) cells in peripheral blood, and their ratio, has been shown to differ predictably in atopics and patients with leprosy, where MT2 correlates with a Th2 phenotype and MT1 with a Th1 phenotype. Stable asthmatics, requiring fluticasone propionate (FP) 750–1000 µg daily or equivalent, were randomized to receive, double‐blinded, either Seretide®[salmeterol and fluticasone propionate (SFC, n = 16)] 50 µg/500 µg bd or FP 500 µg bd (n = 17). If asthma was controlled based on lung function and symptoms at clinic visits every 6 weeks, ICS dose was tapered until asthma exacerbated or 0 µg was reached. The frequency and ratio of MT2 and MT1 T cells of the patients was monitored at 6 week intervals. As treatment tapered, the frequency of MT2 cells decreased (P = 0038 from first to final visit), whereas that of MT1 cells increased. The ratio of MT2/MT1 decreased (P = 0049 from first to final visit). In patients receiving LABA + ICS, the fall in MT2/MT1 ratio appeared to be more pronounced than in patients receiving ICS alone. Thus, the MT2 phenotype may be associated with stable asthma, whereas an imminent exacerbation may associate with an increase in the MT1 phenotype. LABA may allow for a greater effect of FP on the MT ratio.

Limited long-term naive CD4+ T cell reconstitution in patients experiencing viral load rebounds during HAART.

Long-term (3.5 years) immune reconstitution in relation to viral load response was determined. Plasma HIV-1 RNA was suppressed in 40 patients (full responders) up to 42 months, and 17 patients achieved partial response. The measurements of CD4(+) and CD8(+) T lymphocyte subsets (CD45RA, CD45RACD62L, CD45RO, CD28, CD38) were carried out by flow cytometry. Full responders had a significant increase of CD4(+) and all CD4(+) T subsets both up to 6 and from 6 to 42 months, while the increase for partial responders was only up to 6 months. By 6 months, higher slopes were observed in full versus partial responders in the % of CD28 on CD4(+) and the % of CD4(+) memory subset and in both naïve and memory CD4(+) subsets from 6 to 42 months. The percentage of CD8(+) and its subsets was decreased significantly in full responders both up to 6 and from 6 to 42 months (except for an increase in the CD8(+)CD45RA(+) CD62L(+) cells), while in partial responders this decrease was only up to 6 months. Lower slopes were observed in full versus partial responders from 6 to 42 months in the percentages of CD8(+), CD8(+)CD45RO(+), CD8(+)CD28(-), and CD8(+)CD38(+) T cells. In conclusion, full responders have a stronger long-term naive CD4(+) T cell subset reconstitution than partial responders.

Evidence of thymic reconstitution after highly active antiretroviral therapy in HIV-1 infection.

We aimed to provide evidence of thymic reconstitution after highly active antiretroviral therapy (HAART) in HIV-1 infected patients and to correlate this with the restoration of peripheral naïve T cells. Positron emission tomography (PET) enables definitive evidence of thymic activity, indicating functional potential. In this case study, a single patient who initiated HAART demonstrated reconstitution of the naïve T-cell pool and underwent thymic PET scans at baseline and 2 and 6 months following initiation of therapy. Two patients who failed to demonstrate such reconstitution acted as controls. These patients (mean age 27 years) had chronic HIV infection with low CD4 T-cell counts (mean 82, range 9-160 cells/microL blood). Increased function of the thymus visualized by PET was correlated with phenotypic changes in CD4 and CD8 T cells in the periphery measured by flow cytometry, and with numbers of recent thymic emigrants measured by quantification of the numbers of T-cell receptor excision circles (TRECs) in peripheral cells. In one patient, clear correlations could be drawn between visible activity within the thymus, as measured by increased [F18]fluorodeoxyglucose (FDG) uptake, and regeneration of naïve CD4 (CD45RA/CD62L) T cells, increased numbers of CD4 T cells, controlled viraemia and increased numbers of recent thymic emigrants. A second patient displayed no increase in peripheral CD4 count and no increase in thymic activity. The third patient elected to stop therapy following the 2-month time point. The use of PET suggests that thymic activity may increase after HAART, indicating that the thymus has the potential to be functional even in HIV-1 infected persons with low CD4 T-cell counts.

IL-15 enhances the function and inhibits CD95/Fas-induced apoptosis of human CD4+ and CD8+ effector-memory T cells.

Although the effect of IL-15 has been described on murine cells in vitro and in vivo, its effect on human memory CD8(+) T cells is not well characterized. We show here that IL-15 preferentially enhances the activation and effector function of human effector-memory CD45RA(-)CD62L(-) and CD45RA(+)CD62L(-) CD4(+) and CD8(+) T cells in both healthy and HIV-infected individuals. We find that IL-15 increases 2- to 5-fold both the activation and secretion of the effector cytokines IFN-gamma and tumor necrosis factor (TNF)-alpha by anti-CD3-stimulated purified CD4(+) and CD8(+) T cells and peripheral blood mononuclear cells from healthy and HIV-infected individuals. Furthermore, IL-15 potently inhibits CD95/Fas-induced apoptosis of the effector-memory CD4(+) and CD8(+) T cells from HIV-infected individuals. These findings suggest that in addition to being a growth and survival factor for memory CD8(+) T cells, IL-15 is also a potent activator of human effector-memory CD8(+) T cells both in healthy and in HIV-infected individuals.

Dysregulated lymphocyte proliferation and differentiation in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, inflammatory disease of the synovium of uncertain pathogenesis. A number of phenotypic and functional T-cell defects have been described in RA, including abnormal clonal expansions and suppressed proliferative responses, which suggest a defect in T-cell differentiation. Here, we show that RA patients possess fewer naive CD4(+) T cells than healthy controls. Furthermore, a smaller proportion of these cells contains a T-cell receptor excision circle (TREC). Patients with RA also have unusual populations of T cells. These include immature cells characterized as CD45RB(bright)CD45RA(+)CD62L(-) by flow cytometry and a large population that coexpresses CD45RA and CD45RO. These cells are hyperresponsive to mitogen and TCR stimulation when compared to naive cells. Additionally, an unusual putative central memory subset expressing CD62L, but not CD45RA, appears in RA patients at the expense of more typical cells. Levels of C-reactive protein correlate inversely with the TREC content of naive T cells and positively with the sizes of naive and immature atypical T-cell subsets. These data suggest that inflammation drives proliferation of naive T cells in RA and encourages their differentiation into atypical, hyperresponsive progeny. TREC content of individual naive and atypical T-cell subsets suggests an ontogeny consistent with this hypothesis. These studies provide further evidence of a T-cell differentiation defect in RA, which could explain some of the well-characterized immunologic features of the disease.

Characterizing immune reconstitution after long-term highly active antiretroviral therapy in pediatric AIDS.

In this study, we sought to characterize the T lymphocyte recovery in vertically HIV-1-infected children who respond to long-term highly active antiretroviral therapy (HAART). A 3-year longitudinal retrospective study was used to perform a cross-sectional study of 32 children rated according to the time course of CD4(+) T cell percentages in response to antiretroviral therapy and CDC clinical classification: (1) long-term asymptomatic (LTA group): 8 children in A1 during the whole follow-up period; (2) responsive to HAART (Rec group): 13 children in C3 before HAART who achieved CD4(+) T cell counts of > 500 cells/mm(3) after 3 years of HAART; and (3) nonresponsive to HAART (Non-Rec group): 11 children in C3 during the whole follow-up period despite 3 years of HAART. We also studied 17 healthy age-matched uninfected children as controls. Lymphoproliferative responses (LPRs) were evaluated by incorporation of [(3)H]thymidine, identification of T cell subsets by three-color flow cytometry, and determination of thymic production of T cells by quantification of T cell receptor rearrangement excision circles (TRECs). Interestingly, the Rec group showed an increase in percentage of CD4(+) T cells and a decrease in viral load, and recovered LPRs to mitogens and recall antigens, with values similar to those of the LTA group. Moreover, the Rec group produced similar percentages and absolute counts of naive (CD45RA(+)CD62L(+)) CD4(+) and CD8(+) T cells, and TRECs similar to those of the LTA group. In particular, the Rec group produced similar percentages of CD8(+)CD28(-)CD57(+) and CD8(+)CD28(-)CD57(-) T cell subsets compared with controls. Our data indicate that among children who have already progressed to AIDS and severe immunodeficiency but who respond to HAART, the immune system can recover and resemble those of nonprogressors or even uninfected children, in quantitative as well as in functional terms.

Increasing CD4+ T cells specific for tuberculosis correlate with improved clinical immunity after highly active antiretroviral therapy.

Treatment advances have led to dramatic clinical improvements for patients with HIV-1 infection. These clinical improvements reflect treatment-related improvements in immune function, which are most striking in individuals who develop exaggerated immune inflammatory responses to occult opportunistic infections. The mechanisms accounting for these exaggerated immune responses are unknown. To gain insight into these mechanisms, we intensively studied a subject untreated for disseminated tuberculosis and HIV-1 coinfection who then began treatment for both diseases. We examined the changing frequencies of Mycobacterium tuberculosis (MTB)-specific CD4(+) T cells that produced interferon gamma (IFN-gamma) after short-term stimulation with MTB antigen, and we compared these frequencies with those in HIV-1-seronegative subjects with and without prior exposure to MTB antigens. For the HIV-1/MTB-coinfected subject, the proportion of peripheral blood CD4(+) T cells expressing MTB-specific IFN-gamma was 8.6% at 11 days, 11% at 33 days, and 33% at 95 days after starting treatment for HIV-1. CD4(+) IFN-gamma(+) T cells had a CD45RA(-)CD62L(-) (effector memory) phenotype and most coexpressed interleukin 2. Median frequencies of CD4(+) IFN-gamma(+) T cells from six subjects without and nine subjects with prior exposure to MTB antigens were 0.06 and 0.46%, respectively. We conclude that individuals starting treatment for disseminated tuberculosis and HIV-1 coinfection can accumulate remarkably large numbers of MTB-specific CD4(+) T cells in the peripheral blood. The rapid expansion of antigen-specific effector CD4(+) T cells is one mechanism to explain immediate improvements in clinical immunity after HIV-1 treatment. This mechanism provides a theoretical framework to understand the unusual inflammatory responses recently reported to occur after starting HIV-1 treatment.

Assessment of thymic output in common variable immunodeficiency patients by evaluation of T cell receptor excision circles.

Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by repeated infections and hypogammaglobulinaemia. Additionally, T-cell abnormalities including lymphopenia, decreased proliferation to mitogens and antigens, and the reduced production and expression of cytokines, have also been observed. In this study we have investigated the expression of naive, memory and activation markers in T-cell subpopulations in 17 CVID patients in comparison to age-matched normal controls. The numbers of CD4+ T cells, including CD45RA+CD62L+ and, to a lesser extent, CD45RA-CD62L+/RA+CD62L- were significantly reduced in patients, whereas CD8+ T cells were within normal range. In contrast, HLA-DR+ cells were increased both in CD4+ and CD8+ T cells. To assess the thymic output, we analysed the presence of T-cell receptor excision circles (TRECs) in CD4+ and CD8+ T cells by quantitative PCR. TRECs were decreased significantly in patients and the rate of TREC loss was higher with increasing age. TRECs correlated with naive CD4+ T cells, whereas there was an inverse relationship between TRECs and CD8+HLA-DR+ and CD8+CD45RA-CD62L+/RA+CD62L- T cells. Our results suggest the presence of a defect in the naive T cell compartment with origin at the thymic level in CVID, and indicate that TREC may be a useful marker to monitor thymic function in this primary immunodeficiency.

Evaluation of thymopoiesis using T cell receptor excision circles (TRECs): differential correlation between adult and pediatric TRECs and naïve phenotypes.

To determine whether the thymus is still functional despite age-related involution, we measured a biomarker for thymopoiesis known as the T cell receptor excision circle (TREC) from peripheral blood mononuclear cells (PBMCs) of 148 healthy children and from PBMCs, CD4(+), and CD8(+) cells of 32, 30, and 50 healthy adults, respectively. We demonstrate that during the first 5 years of life, thymic output is decreased (P 0.002) but not dramatically (r = -0. 282). Among adults aged 23-58, thymic output was inversely correlated with age, as measured from PBMCs (r = -0.628, P < 0.0005), CD4(+) (r = -0.530, P 0.003), and CD8(+) fractions (r = -0.385, P 0. 006). A strong correlation existed between pediatric PBMC TRECs and the expression of three naïve phenotypic markers (CD45RA(+)CD45RO(-), CD45RA(+)CD62L(+), and CD45RO(-)CD27(+)CD95(low)). Adult PBMC TRECs correlated only with the expression of CD45RA(+)CD45RO(-) (r = 0.459, P 0.012). Our data suggest that in adults CD45RA(+)CD45RO(-) may be enriched for TRECs and add to a growing body of evidence illustrating intact thymic function in adulthood.

Preservation of lymphocyte immunophenotype and proliferative responses in cryopreserved peripheral blood mononuclear cells from human immunodeficiency virus type 1-infected donors: implications for multicenter clinical trials. The ACTG Immunology Advanced Technology Laboratories.

Human immunodeficiency virus type 1 (HIV-1) infection results in impaired immune function that can be measured by changes in immunophenotypically defined lymphocyte subsets and other in vitro functional assays. These in vitro assays may also serve as early indicators of efficacy when new therapeutic strategies for HIV-1 infection are being evaluated. However, the use of in vitro assays of immune function in multicenter clinical trials has been hindered by their need to be performed on fresh specimens. We assessed the feasibility of using cryopreserved peripheral blood mononuclear cells (PBMC) for lymphocyte immunophenotyping and for lymphocyte proliferation at nine laboratories. In HIV-1-infected patients with moderate CD4(+) lymphocyte loss, the procedures of density gradient isolation, cryopreservation, and thawing of PBMC resulted in significant loss of CD19(+) B cells but no measurable loss of total T cells or CD4(+) or CD8(+) T cells. No significant changes were seen in CD28(-) CD95(+) lymphocytes after cell isolation and cryopreservation. However, small decreases in HLA-DR(+) CD38(+) lymphocytes and of CD45RA(+) CD62L(+) were observed within both the CD4(+) and CD8(+) subsets. Fewer than 10% of those specimens that showed positive PBMC proliferative responses to mitogens or microbial antigens lost their responsiveness after cryopreservation. These results support the feasibility of cryopreserving PBMC for immunophenotyping and functional testing in multicenter AIDS clinical trials. However, small changes in selected lymphocyte subsets that may occur after PBMC isolation and cryopreservation will need to be assessed and considered in the design of each clinical trial.

Differential representations of memory T cell subsets are characteristic of polarized immunity in leprosy and atopic diseases.

We identified functionally polarized subsets of CD4 memory T cells on the basis of the expression of CD11a, CD45RA and CD62L. Within the several phenotypically distinct subsets of CD4 memory cells are two that, upon stimulation, produce primarily IL-4 (MT(2), CD45RA(-)CD62L(+)CD11a(dim)) or primarily IFN-gamma (MT(1), CD45RA(-)CD62L(-)CD11a(bright)). In addition, four other phenotypically distinct subsets of CD4 cells have unique cytokine profiles. To determine the clinical relevance of the representation of these cell types, we analyzed blood from patients with the chronic diseases leprosy and atopy. These diseases are characterized as immunologically polarized, since T cell responses in affected individuals are often strongly biased towards T(h)1 (dominated by IFN-gamma production) or T(h)2 (IL-4 production). We show here that this polarization reflects homeostatic or differentiation mechanisms affecting the representation of the functionally distinct subsets of memory CD4 T cells, MT(1) and MT(2). Significantly, the representation of the MT(1) and MT(2) subsets differs dramatically between subjects with tuberculoid leprosy (a T(h)1 disease), or lepromatous leprosy or atopic disease (T(h)2 diseases). However, there was no difference in the cytokine profiles of these or any of the other finely resolved CD4 subsets, when compared between individuals across all disease states. Thus, it is the representation of these subsets in peripheral blood that is diagnostic of the polarized state of the immune system.