Role and Function of T Cell-Derived Exosomes and Their Therapeutic Value.

Exosomes are membrane-bound extracellular vesicles that are produced in the endosomal compartment of most eukaryotic cells. Containing proteins, RNA, and DNA, exosomes mediate intercellular communication between different cell types by transferring their contents and thus are involved in numerous physiological and pathological processes. T cells are an indispensable part of adaptive immunity, and the functions of T cell-derived exosomes have been widely studied. In the more than three decades since the discovery of exosomes, several studies have revealed that T cell-derived exosomes play a novel role in cell-to-cell signaling, especially in inflammatory responses, autoimmunity, and infectious diseases. In this review, we will summarize the function of T cell-derived exosomes and their therapeutic potential.

A modified flow cytometry method for objective estimation of human CD4+ regulatory T cells (CD4+ Tregs) in peripheral blood, via CD4/CD25/CD45RO/FoxP3 labeling.

BACKGROUND: Several methods exist for flow-cytometric estimation of human peripheral blood CD4+ T regulatory cells (CD4+ Tregs). METHODS: We report our experience with the estimation of human CD4+ Tregs via three different characterizations using flow cytometry (CD25high FoxP3+ , CD25high CD127low/- FoxP3+ , and CD4+ CD25high/int CD45ROFoxP3+ ) in normal subjects. We have used these methods on the control populations from two studies (32 and 36 subjects, respectively), the latter two methods retrospectively on the subjects of the first study. The six CD4+ T cell fractions obtained by the third method were differentially colored to ascertain the distribution of these cell fractions in the CD25/FoxP3, CD45RO/FoxP3, and CD25/CD127 dot plots from CD4/CD25/CD45RO/FoxP3 and CD4/CD25/CD45RO/CD127 panels. RESULTS: Each approach gives significantly different estimates of Tregs (expressed as percentage of CD4+ T cells), with the second almost invariably yielding higher percentages than the other two. Only the third approach can distinguish among effector and naïve Tregs and FoxP3+ non-Tregs. Analysis of CD25/CD127 dot plots reveals that Treg delineation via the widely used definition of CD4+ CD25high CD127low/- cells unavoidably yields a mixture of nearly all effector and most of naïve Tregs, as well as FoxP3+ non-Tregs plus other cells. Delineation of effector/naïve Tregs and FoxP3+ non-Tregs is possible via CD45RO/CD25 dot plots but not by CD45RO/FoxP3 counterparts (as done previously) because of overlapping FoxP3 intensities among Tregs and non-Tregs. CONCLUSION: Our comparison shows that CD4/CD25/CD45RO/FoxP3 panels are an objective means of estimating effector and naïve Tregs via colored dot plots, aiding thus in Treg delineation in health and detecting aberrations in disease.

Hepatocytes Delete Regulatory T Cells by Enclysis, a CD4+ T Cell Engulfment Process.

CD4+ T cells play critical roles in directing immunity, both as T helper and as regulatory T (Treg) cells. Here, we demonstrate that hepatocytes can modulate T cell populations through engulfment of live CD4+ lymphocytes. We term this phenomenon enclysis to reflect the specific enclosure of CD4+ T cells in hepatocytes. Enclysis is selective for CD4+ but not CD8+ cells, independent of antigen-specific activation, and occurs in human hepatocytes in vitro, ex vivo, and in vivo. Intercellular adhesion molecule 1 (ICAM-1) facilitates T cell early adhesion and internalization, whereas hepatocytes form membrane lamellipodia or blebs to mediate engulfment. T cell internalization is unaffected by wortmannin and Rho kinase inhibition. Hepatocytes engulf Treg cells more efficiently than non-Treg cells, but Treg cell-containing vesicles preferentially acidify overnight. Thus, enclysis is a biological process with potential effects on immunomodulation and opens a new field for research to fully understand CD4+ T cell dynamics in liver inflammation.

Resolvin D1 Programs Inflammation Resolution by Increasing TGF-ß Expression Induced by Dying Cell Clearance in Experimental Autoimmune Neuritis.

UNLABELLED: Experimental autoimmune neuritis (EAN) is the animal model of human acute inflammatory demyelinating polyradiculoneuropathies (AIDP), an auto-immune inflammatory demyelination disease of the peripheral nervous system (PNS) and the world's leading cause of acute autoimmune neuromuscular paralysis. EAN and AIDP are characterized by self-limitation with spontaneous recovery; however, endogenous pathways that regulate inflammation resolution in EAN and AIDP remain elusive. A pathway of endogenous mediators, especially resolvins and clearance of apoptotic cells, may be involved. Here, we determined that resolvin D1 (RvD1), its synthetic enzyme, and its receptor were greatly increased in PNS during the recovery stage of EAN. Both endogenous and exogenous RvD1 increased regulatory T (Treg) cell and anti-inflammatory macrophage counts in PNS, enhanced inflammation resolution, and promoted disease recovery in EAN rats. Moreover, RvD1 upregulated the transforming growth factor-ß (TGF-ß) level and pharmacologic inhibition of TGF-ß signaling suppressed RvD1-induced Treg cell counts, but not anti-inflammatory macrophage counts, and RvD1-improved inflammation resolution and disease recovery in EAN rats. Mechanistically, the RvD1-enhanced macrophage phagocytosis of apoptotic T cells leading to reduced apoptotic T-cell accumulation in PNS induced TGF-ß production and caused Treg cells to promote inflammation resolution and disease recovery in EAN. Therefore, these data highlight the crucial role of RvD1 as an important pro-resolving molecule in EAN and suggest its potential as a therapeutic target in human neuropathies. SIGNIFICANCE STATEMENT: Experimental autoimmune neuritis (EAN) is the animal model of human acute inflammatory demyelinating polyradiculoneuropathies, an auto-immune inflammatory demyelination disease of the peripheral nervous system (PNS) and the world's leading cause of acute autoimmune neuromuscular paralysis. Here, we demonstrated that resolvin D1 (RvD1) promoted macrophage phagocytosis of apoptotic T cells in PNS, thereby upregulating transforming growth factor-ß by macrophages, increased local Treg cell counts, and finally promoted inflammation resolution and disease recovery in EAN. These data highlight the crucial role of RvD1 as an important pro-resolving molecule in EAN and suggest that it has potential as a therapeutic target in human neuritis.

Levels of regulatory T cells CD69(+)NKG2D(+)IL-10(+) are increased in patients with autoimmune thyroid disorders.

Regulatory T (Treg) cells play an important role in the pathogenesis of autoimmune thyroid disorders (AITD). New subsets of CD4(+)CD69(+) and CD4(+)NKG2D(+) T lymphocytes that behave as regulatory cells have been recently reported. The role of these immunoregulatory lymphocytes has not been previously explored in AITD. We analyzed by multi-parametric flow cytometry different Treg cell subsets in peripheral blood from 32 patients with AITD and 19 controls, and in thyroid tissue from seven patients. The suppressive activity was measured by an assay of inhibition of lymphocyte activation. We found a significant increased percentage of CD4(+)CD69(+)IL-10(+), CD4(+)CD69(+)NKG2D(+), and CD4(+)CD69(+)IL-10(+)NKG2D(+) cells, in peripheral blood from GD patients compared to controls. The increase in CD4(+)CD69(+)IL-10(+) and CD4(+)CD69(+)IL-10(+)NKG2D(+) T cells was especially remarkable in patients with active Graves' ophthalmopathy (GO), and a significant positive correlation between GO activity and CD4(+)CD69(+)IL-10(+) or CD4(+)CD69(+)IL-10(+)NKG2D(+) cells was also found. In addition, these cells were increased in patients with a more severe and/or prolonged disease. Thyroid from AITD patients showed an increased proportion of CD69(+) regulatory T cells subpopulations compared to autologous peripheral blood. The presence of CD69(+), NKG2D(+), and IL-10(+) cells was confirmed by immunofluorescence microscopy. In vitro functional assays showed that CD69(+) Treg cells exerted an important suppressive effect on the activation of T effector cells in controls, but not in AITD patients. Our findings suggest that the levels of CD69(+) regulatory lymphocytes are increased in AITD patients, but they are apparently unable to down-modulate the autoimmune response and tissue damage.

Subcellular localization of FOXP3 in human regulatory and nonregulatory T cells.

The transcriptional regulator FOXP3 is an important determinant of regulatory T (Treg) cell development and function and is frequently used to quantitate Treg cells. However, FOXP3 is also expressed in recently activated conventional human T cells. Here, we investigated the FOXP3 expression patterns in Treg and activated T cells at a cellular level. Upon activation, human CD4(+) CD25(-) T cells expressed FOXP3 mainly in the cytoplasm, in sharp contrast to human CD4(+) CD25(+) Treg cells, where we found FOXP3 to be predominantly expressed in the nucleus. A GFP-FOXP3-fusion protein shuttled from the nucleus to the cytoplasm in transfected primary human T cells. We identified two novel leucine-rich nuclear export signals in FOXP3. Site-directed mutagenesis of both sequences completely abolished nuclear export of FOXP3 in human T cells. Both export sequences localized to exons affected by alternative splicing. The three isoforms FOXP3Δ2, FOXP3Δ7, and FOXP3Δ2Δ7 localized preferentially to the nucleus. Additionally, forced expression of nucleus-directed FOXP3 induced a Treg-cell-associated gene expression pattern and induced regulatory capacity. These findings should aid in the interpretation of future studies utilizing FOXP3 expression as a Treg-cell marker and shed some light on the molecular mechanisms controlling subcellular FOXP3 localization in human T cells.

Single-cell dynamics of mast cell-CD4+ CD25+ regulatory T cell interactions.

The biological behavior of immune cells is determined by their intrinsic properties and interactions with other cell populations within their microenvironment. Several studies have confirmed the existence of tight spatial interactions between mast cells (MCs) and Tregs in different settings. For instance, we have recently identified the functional cross-talk between MCs and Tregs, through the OX40L-OX40 axis, as a new mechanism of reciprocal influence. However, there is scant information regarding the single-cell dynamics of this process. In this study, time-lapse video microscopy revealed direct interactions between Tregs and MCs in both murine and human cell co-cultures, resulting in the inhibition of the MC degranulation response. MCs incubated with WT, but not OX40-deficient, Tregs mediated numerous and long-lasting interactions and displayed different morphological features lacking the classical signs of exocytosis. MC degranulation and Ca2+ mobilization upon activation were inhibited by Tregs on a single-cell basis, without affecting overall cytokine secretion. Transmission electron microscopy showed ultrastructural evidence of vesicle-mediated secretion reconcilable with the morphological pattern of piecemeal degranulation. Our results suggest that MC morphological and functional changes following MC-Treg interactions can be ascribed to cell-cell contact and represent a transversal, non-species-specific mechanism of immune response regulation. Further research, looking at the molecular composition of this interaction will broaden our understanding of its contribution to immunity.

Cell-in-cell structures formed between human cancer cell lines and the cytotoxic regulatory T-cell line HOZOT.

We previously established a novel cell line, termed HOZOT, derived from umbilical cord blood mononuclear cells that is characterized as a human cytotoxic regulatory T (Treg) cell line with a FOXP3(+)CD4(+)CD8(+)CD25(+) phenotype. Here, we describe a new property of HOZOT cells: they actively penetrate into a variety of human cancer cell lines, but not into normal cell lines, and form apparent cell-in-cell structures. In the process of cell penetration, we observed that HOZOT cells adhered to target cells seemed to first insert their nuclei into the cytoplasm of target cells, distinct from the process of phagocytosis. In addition, blocking experiments showed that major histocompatibility complex class I is one of the target cell recognition molecules for HOZOT cells. Furthermore, we propose that cell-in-cell structures between HOZOT cells and target cancer cells could be one of the cytotoxic mechanisms of HOZOT cells.

Segmented filamentous bacteria take the stage.

Commensal bacteria are crucial for maturation and function of the mucosal immune system. However, the mechanisms of these interactions are poorly understood. In addition, the role of the composition of the microbiota and the importance of individual species in this community in stimulating different types of immunity are major unanswered questions. We recently showed that the balance between two major effector T cell populations in the intestine, IL-17(+) Th17 cells and Foxp3(+) Tregs, requires signals from commensal bacteria and is dependent on the composition of the intestinal microbiota. Comparison of microbiota from Th17 cell-deficient and Th17 cell-sufficient mice identified segmented filamentous bacteria (SFB) as capable of specifically inducing Th17 cells in the gut. SFB represent the first example of a commensal species that can skew the mucosal effector T cell balance and thus affect the immune fitness of the individual.

Chromatin remodeling complex in Treg function.

Regulatory T cells (Treg), formerly known as suppressor T cells, are essential for maintaining self-tolerance as well as immune homeostasis. Lack of Treg or normal function of Treg often leads to lymphoproliferative syndrome and autoimmunity in human and mouse. The chromatin remodeling BAF complex regulates gene expression through the activity of Brg. Genetic ablation of Brg gene in mouse resulted in early embryonic lethality. T cell failed to develop in the thymus when Brg is deleted at DN stage. Using a Brg conditional KO mouse model, we deleted Brg at the DP stage in the thymus. Unexpectedly, T cells developed and matured normally. However, these mice displayed lympho-proliferative syndrome 2-4 months of age with enlarged peripheral lymphoid organs and leukocyte infiltration in non-lymphoid organs. T cells from these mice turned into effector cells producing increased amounts of effector cytokines as early as 4 weeks after birth. Further analysis revealed that the Treg population was specifically affected by Brg deletion. In this mini-review, we will discuss in detail the properties of Tregs controlled by Brg and the potential underlying mechanisms for an unanticipated, specific role of the Brg-containing BAF complex in controlling Treg functions.

MRL/Mp CD4+,CD25- T cells show reduced sensitivity to suppression by CD4+,CD25+ regulatory T cells in vitro: a novel defect of T cell regulation in systemic lupus erythematosus.

OBJECTIVE: To investigate the hypothesis that loss of suppression mediated by peripheral CD4+,CD25+ regulatory T cells is a hallmark of systemic lupus erythematosus (SLE). METHODS: Mice of the MRL/Mp strain were studied as a polygenic model of SLE. Following immunomagnetic selection, peripheral lymphoid CD25+ and CD25- CD4+ T cells were cultured independently or together in the presence of anti-CD3/CD28 monoclonal antibody-coated beads. Proliferation was assessed by measuring the incorporation of tritiated thymidine. RESULTS: While MRL/Mp CD4+,CD25+ regulatory T cells showed only subtle abnormalities of regulatory function in vitro, syngeneic CD4+,CD25- T cells showed significantly reduced sensitivity to suppression, as determined by crossover experiments in which MRL/Mp CD4+,CD25- T cells were cultured with H-2-matched CBA/Ca CD4+,CD25+ regulatory T cells in the presence of a polyclonal stimulus. CONCLUSION: Our findings highlight a novel defect of peripheral tolerance in SLE. Identification of this defect could open new opportunities for therapeutic intervention.

[The drug "Selena" in the complex treatment of patients with chronic inflammatory diseases of the biliary system]. / Preparat "Selena" v kompleksnomu likuvanni khvorykh na khronichni zapal'ni zakhvoriuvannia biliarnoï systemy.

The drug selena of the Novamed firm has been shown to be of high clinical, biochemical, and immunological effectiveness in a combined treatment of patients with chronic inflammatory diseases of the biliary system presenting with immunological disorders, that was evidenced by a sooner than in controls disappearance or alleviation of clinical manifestations of the disease, normalization of clinical indices for blood, ultrastructure of the immunocompetent cells, and by less time for the functional state of the liver to return to normal. It is suggested that the drug effect on the immune system might be mediated through normalization of lipid peroxidation and of the system for antioxidant defence.

The duration of antigenic stimulation determines the fate of naive and effector T cells.

It is known that T cells engage antigen-presenting cells (APCs) in a stable interaction that results in sustained TCR signaling. We show here that the duration of this process is critical in determining whether T cells will be activated or deleted. Whereas naive T cells require approximately 20 hr of sustained signaling to be committed to proliferation, effector T cells become committed after only 1 hr but die following activation if antigenic stimulation is prolonged. Costimulation by anti-CD28 facilitates T cell activation by decreasing the time of commitment and by protecting T cells from death. These findings explain in quantitative terms the essential requirement for professional APCs in T cell priming and show that the duration of antigenic stimulation is the major factor determining the fate of naive and effector T cells.

Analysis of antitumor properties of effector cells stimulated with a cell wall preparation (WPG) of Bifidobacterium infantis.

Intestinal Bifidobacterium species are thought to be beneficial in animal and human intestines. We studied the mechanisms of Bifidobacteria in antitumor activity using a cell wall preparation (WPG) of B. infantis (Cancer Res., 45, 1300, (1985)). WPG enhanced the in vitro antitumor activities of mouse peritoneal exudate cells elicited with proteose-peptone (P-PEC) and thioglycollate broth (TG-PEC), determined by cytostatic ([3H]thymidine uptake inhibition) and cytolytic ([3H]uridine release) assays. Tumor necrosis factor-alpha (TNF-alpha) and reactive nitrogen intermediates (RNI) play a role in such augmented cytotoxicity, because anti-TNF-alpha antibody almost completely blocked the increased cytolytic activity of P-PEC in the presence of WPG. Moreover, WPG induced RNI in the supernatant of TG-PEC in a dose-dependent manner. The mRNA expression of several cytokines (IL-1 beta, IL-6, IL-10, IFN-alpha and TNF-alpha) was induced in BALB/c mouse peritoneal cells 3 h after an intraperitoneal injection of WPG (3 h WPG-PEC). However, this expression disappeared from 24 h WPG-PEC, except for that of IFN-alpha. IFN-gamma was not induced. Kinetic studies of the tumor neutralizing activities of the WPG-PECs by means of the in vivo Winn assay revealed that the activity emerged at 1.5 h, became maximal at 3 h and disappeared at 24h. These results indicated that Bifidobacterial WPG is a Biological Response Modifier (BRM) with characteristics similar to those of other bacterial BRMs.

In vivo and in vitro suppression of T-cell receptor alpha/beta CD4- CD8- T lymphocytes by cyclosporine A.

We treated a patient with a combined immunodeficiency and disease pathology resembling GvHD with cyclosporine. This disorder was characterized by exfoliative dermatitis, lymphadenopathy, and lymphocytosis of a novel T-cell phenotype (CD3+ TCR alpha/beta+ CD4- CD8-). The patient's peripheral blood T cells had elevated cytolytic activity and expressed increased levels of IL2R, HLA-DR, and CD45RO. Treatment with CsA resulted in marked clinical improvement, resolution of the lymphocytosis, and reduced cytolytic activity of peripheral blood T cells. T-cell HLA-DR and IL2R expression was reduced by cyclosporine, but CD45RO remained intact on virtually all circulating T cells. CsA also inhibited the cytolytic activity and cytokine production of in vitro cultured TCR alpha/beta+ CD4- CD8- cell lines. Our data suggest that alleviation of the patient's clinical symptoms resulted from cyclosporine-mediated suppression of proliferation, cytotoxicity, and inflammatory cytokine production of TCR alpha/beta+ CD4- CD8- T lymphocytes in vivo. The response of this patient to cyclosporine, which was similar to that seen in true GvHD, provides further evidence that these conditions share common pathogenetic pathways.

Soluble interleukin 2 receptor release, interleukin 2 production, and interleukin 2 receptor expression in activated T-lymphocytes in vitro.

Following activation in vitro, peripheral blood mononuclear cells (PBMC) express cell-associated interleukin-2 receptors (IL2R). The present study was undertaken to define the proportion of T lymphocyte subsets that express the IL2R (CD25 antigen) upon different mitogenic stimulation. Double immunofluorescence staining with different fluorochromes, fluorescein isothiocyanate and phycoethyrin, was applied for identification of IL2R positive cells and individual lymphocyte subset. The exact percentage of individual activated lymphocyte subset bearing IL2R was enumerated by photographic counting. There was paucity of IL2R in freshly isolated, unstimulated peripheral blood, PBMC cultured without mitogen, and cultured B lymphocytes. Following pokeweed mitogen stimulation in vitro, 19% of CD4 (T-helper/inducer) lymphocytes and 14% of CD8 (T-suppressor/cytotoxic) lymphocytes expressed IL2R. Similarly, 25% of CD4 lymphocytes and 19% of CD8 lymphocytes expressed IL2R following phytohemagglutinin stimulation in vitro. Contrary to the reported data of Tac-positive cells in human lymphoid tissues, our study revealed that, upon lectin mitogen stimulation, approximately 55% of IL2R positive PBMC were CD4 lymphocytes, and 45% of them were CD8 lymphocytes. These observations imply the plausible notion that interleukin-2 mediated immune activation of T lymphocytes in PBMC is different from that in local lymphoid organs. It was also demonstrated that the release of soluble IL2R (sIL2R) and IL2 production in supernatant from cultured PBMC varied with different lectin stimulation. A significant correlation was demonstrated between the cellular and soluble IL2R but the production of IL2 from activated mononuclear cells bore no good correlation with either the cellular IL2R expression or the release of sIL2R.

Omental dendritic cells: Ia expression and relation to macrophages.

Rat omental dendritic cells (ODC) occur in two forms, mainly spindle-shaped, Ia-, on the surface, and stellar, Ia+ within the omentum. Like macrophages, most ODC label with W3/25 mAb and have a demonstrable activity of non-specific esterase, acid phosphatase and ATPase. Up to 30% of ODC are actively phagocytic. The proportion of Ia+ ODC rises 7 days after ip antigenic stimulation and there seems to be a reciprocal development of Ia positivity and phagocytic capacity between ODC and macrophages 3 and 5 days after ip immunization. ODC contribute to the overall fluctuation of Ia expression in the entire omentum after immunization. Ia+ ODC display a linear arrangement along preilymphatic spaces and may be related to the formation of new lymph vessels. They also constitute the stroma of pseudofollicles containing clusters of what are presumably T-helper lymphocytes closely attached to ODC, scattered suppressor T lymphocytes and B cells accumulating in later stages at the immune response.

Tannic-acid staining material on high endothelial venules and lymphocytes in skin and peripheral lymph nodes in Staphylococcus aureus-associated erythroderma.

The recognition and binding of glycoprotein receptors on lymphocytes to specific antigens present on high endothelial venules (HEV) precedes the egress of lymphocytes from the blood stream into the tissues. In this paper, we report the presence of HEVs with tannic-acid staining material (TASM+ HEVs) in Staphylococcus aureus-associated erythroderma, which allow the migration of CD8+ lymphocytes from the bloodstream into the epidermis. TASM positivity is also expressed on lymphocytes within the regional lymph nodes, and by intravascular lymphocytes prior to leaving the TASM+ HEV. It is proposed that TASM positivity may represent a molecule, which may function in binding lymphocytes to HEVs prior to egress from the HEV. (TASM is lost from lymphocytes after leaving the HEVs). The expression of TASM positivity may form an essential part of the CD8+ lymphocyte-HEV recognition system, and may be the means whereby CD8+ lymphocytes generated in the regional lymph nodes by various mitogens (in this case by staphylococcal mitogens) may 'home' to specific sites within the epidermis. TASM positivity on both the HEVs and lymphocytes may serve as a convenient marker of such a system.

Characterization of a new strain of HHV-6 (HHV-6SF) recovered from the saliva of an HIV-infected individual.

An isolate of the human herpesvirus-6 (HHV-6SF) recovered from the saliva of an HIV-infected individual differs in its cellular host range and certain genomic properties from other HHV-6 strains described. HHV-6SF replicates in adult peripheral blood mononuclear cells (PMC) substantially better than in fetal cord blood PMC and can be grown only in the MT-4 established T cell line. It preferentially infects CD4+ lymphocytes but can replicate in CD8+ cells and peripheral blood macrophages. It also infects neuroblastoma cells and cell lines derived from the gastrointestinal tract. These latter results suggest that this herpesvirus could play a role in disorders affecting these tissues. Finally, the restriction enzyme pattern of HHV-6SF differs from that of other HHV-6 strains. The identification of this distinct HHV-6 strain could indicate an unusual biologic variation among viral isolates thus far not observed with other herpesviruses.

Mechanism in 1,25(OH)2D3-induced suppression of helper/suppressor function of CD4/CD8 cells to immunoglobulin production in B cells.

On the basis of previous data that 1,25(OH)2D3 suppressed both helper and suppressor activities of CD4 and CD8 cells in the pokeweek mitogen-stimulated culture, we examined the further effect of 1,25(OH)2D3 on both cells to define how 1,25(OH)2D3 is involved in the deterioration of their functions. 1,25(OH)2D3 suppressed the pokeweed mitogen and phytohemagglutinin-induced DNA synthesis of CD4 and CD8 cells. The suppression by 1,25(OH)2D3 of DNA synthesis was caused by a time lag in reaching maximal response. 1,25(OH)2D3 also suppressed interleukin-2 production of CD4 and CD8 cells. 1,25(OH)2D3 did not, however, affect their interleukin-2 receptor expression detected within 24 hr after phytohemagglutinin stimulation. In addition, 1,25(OH)2D3 failed to suppress DNA synthesis of CD4 and CD8 cells when cultured with a large amount of interleukin-2. Suppression by 1,25(OH)2D3 of proliferation and interleukin-2 production in CD4 and CD8 cells would bring about the decrease of their helper or suppressor functions by inhibiting their expansion or maturation.