Divergent effects of thyroid HLA-antigens on T and natural killer (NK) cell cytotoxicity.

We have used non-autoimmune non-neoplastic human thyroid cells to explore the role of surface class I and DR antigens on these cells' sensitivity towards T and Natural Killer (NK) cell cytotoxicity. Non-treated thyrocytes expressed class I but no DR antigens. Following incubation with gamma-interferon (gamma-IFN) class I antigens were markedly elevated and DR expression was induced. Whereas non-treated thyrocytes were minimally lysed by sensitized T cells, they served as appropriate targets for NK cells. Following incubation with gamma-IFN, the thyroid cells became highly sensitive to T cell lysis, with no significant reduction in their vulnerability to NK cell killing. The addition of monoclonal anti class I or DR antigens, or brief acid treatment which specifically eliminates class I molecules, inhibited T cell cytotoxicity but enhanced the sensitivity to lysis by NK cells. Thus, the presence of HLA antigens on the same thyroid cells have an opposite effect on two major cytotoxi mechanisms. Our findings are relevant within the context of recent suggestions of intervening with target HLA antigens for the management of autoimmune and malignant diseases.     

The remarkable proliferation of helper T cell subset in response to autologous thyrocytes and intrathyroidal T cells from patients with graves'' disease

We have studied cellular interactions among thyrocytes, intrathyroidal T cells and peripheral blood T cells from Graves' patients. In the autologous mixed lymphocyte reaction of Graves' patients, CD4+ cells were able to proliferate vigorously against autologous non-T cells, whereas CD8+ cells responded weakly to non-T cell stimulators. Furthermore, the proliferative response of the CD4+ 2H4+ suppressor-inducer T cell subset was increased like that of the CD4+ 2H4- helper T cell subset. In contrast to peripheral blood non-T cell stimulators, thyrocytes and intrathyroidal T cells had the ability to activate the CD4+ 2H4- helper T cell subset but were not able to cause proliferation both of CD4+ 2H4+ suppressor-inducer T cell and CD8+ suppressor/cytotoxic T cell subsets. The marked reduction in proliferative responses of CD4+ 2H4+ cells and CD8+ cells could not be attributed to a difference in kinetics or altered response to variable number of stimulator cells. On the basis of these findings, it is suggested that the concentration of the helper T cell subset may be progressively increased and suppressor circuits may be unable to be activated in thyroid tissues. These abnormalities in cellular interactions may induce the excessive production of autoantibodies.     

Autologous CD8-positive cells suppress T cell proliferation in response to thyroid antigens in Hashimoto's thyroiditis

To assess whether there is a defect in thyroid antigen-specific suppressor cells in Hashimoto's thyroiditis (HT) and whether such cells actively prevent thyroid autoreactivity in control subjects, T cell proliferation was measured before and after removal of CD8-positive cells from the lymphocyte population. CD8 depletion significantly increased the proliferation of HT lymphocytes to soluble thyroglobulin and to thyroid microsomal antigen immunoblotted onto nitrocellulose; some of these cultures also reacted with an unidentified thyroid antigen, mol wt approx 16 kDa. However, CD8 depletion did not permit normal lymphocytes to respond to thyroid antigens. Peripheral blood CD8 cells were also found to suppress proliferation of a thyroid T cell line, derived from a patient with HT, in response to autologous, Ia-positive thyroid follicular cells. These results do not support the existence of a defect in antigen-specific suppressor cells in HT, nor the active suppression of thyroid autoreactivity by such cells in normal subjects. The data suggest that there may be an imbalance in T cell helper and suppressor influences in thyroiditis, but in some patients a new balance is achieved, so that T cell sensitization to thyroid autoantigens can only be identified by removal of CD8-positive cells.     

Synergy in antigen presentation by thyroid epithelial cells and monocytes from patients with graves'' disease

The present study was undertaken to examine the ability of thyrocytes from Graves' patients to present purified protein derivative (PPD) to autologous peripheral blood T cells. Normal human thyrocytes which were pre-cultured with interferon-gamma were able to induce the proliferation of T cells in response to PPD antigen, but unstimulated thyrocytes failed to do. Thyrocytes from Graves' patients on which HLA-DR antigens were expressed have an ability to induce the proliferation of T cells. Thyrocytes from Graves' patients which were pulsed with PPD antigen for 4 h were capable of stimulating proliferation of the T cells. However, the stimulation index of T cells co-cultured with thyrocytes and PPD were significantly lower than that of T cells co-cultured with monocytes and PPD. Sub-optimal numbers of monocytes which by themselves were unable to support T-cell proliferation synergistically augmented antigen presentation by thyrocytes. These results suggest that cellular interactions among thyrocytes, monocytes and T cells may perpetuate immune or autoimmune responses in thyroid tissues from Graves' patients.     

The priming of helper T cells

Before helper T cells and B cells can interact to produce specific antibody, the antigen-specific helper T cell precursors must be primed. Priming is a fairly abrupt event which occurs in vivo about 5 days after immunization. Priming involves several steps: Antigen uptake, processing, and cell surface expression bound to class II MHC molecules by an antigen presenting cell, recirculation and antigen-specific trapping of helper T cell precursors in lymphoid tissue, and T cell proliferation and differentiation. Helper T cells express CD4, but not all CD4 T cells are helper cells. The signals required for clonal expansion of helper T cells differ from those required by other CD4 T cells. The critical antigen-presenting cell for helper T cell priming appears to be a macrophage, and the critical second signal for helper T cell growth is the macrophage product interleukin-1.     

The Effect of Staphylococcal Enterotoxin B on Thyrocyte HLA Molecule Expression

Microbial superantigens have been implicated in the pathogenesis of human autoimmune diseases. In autoimmune glands, thyrocytes inappropriately express HLA-DR molecules and these cells may function as antigen presenting cells (APC) We studied the effect in vitro of staphylococcal enterotoxin B (SEB) on HLA molecule expression on thyrocytes obtained from autoimmune and non-autoimmune glands by immunofluorescence. HLA class I and class II upregulation could be detected by FACS analysis on thyrocytes. Anti-IFN-gamma neutralizing antibodies markedly affect both class I and class II upregulation on thyrocytes. FRTL5 cells were not responsive to SEB. Similarly, a human thyroid cell strain maintained in culture in a conditioned medium was not induced to express HLA products by SEB stimulation. The addition of autologous intrathyroidal lymphocytes caused reestablishment of the SEB effect.     

Thyroid-specific T cells in the normal Wistar rat. I. Characterization of lymph node T cell reactivity to syngeneic thyroid cells and thyroglobulin.

Wistar rats are susceptible to the induction of experimental autoimmune thyroiditis (EAT) and recently a cloned Wistar thyroid epithelial cell line (WRT) has become available. In this study we have examined the in vitro proliferative response of Wistar rat lymphoid cells to the WRT cells as a model for better understanding thyroid cell-T cell interactions. Lymph node (LN) cells from normal Wistar rats showed an early and vigorous response to syngeneic thyroid cells (WRT). Further examination of the Wistar phenomenon revealed that unpurified lymphoid cells were also able to mount a proliferative response to rat thyroglobulin. The Wistar LN cell response to WRT cells consisted of T cell proliferation that was both MHC class I and class II restricted. There was a greater proliferation of CD8+ than CD4+ T cells, but WRT-stimulated lymphoblast cells were not cytotoxic to 51Cr-labeled WRT cell targets. These data suggest that normal Wistar rats have circulating thyroid-specific T cells that may be related to their known susceptibility to EAT. Furthermore, the interaction between such thyroid-specific T cells and cloned syngeneic thyroid cells offers a unique model for the further investigation of thyroid-immune interactions and the escape from tolerance induction.     

A functional and phenotypic study on immune accessory cells isolated from the thyroids of Wistar and autoimmune-prone BB-DP rats

Dendritic cells (DCs) comprise a small population of cells in the normal thyroid. These excellent antigen-presenting cells (APCs) are thought to be involved in the initiation of thyroid autoimmune reactions. However it is not known whether the APCs involved in this process are indeed DCs, or thyrocytes.Our aims were as follows: (1) to isolate DCs from the thyroid of normal Wistar rats and BB-DP rats prior to the development of lymphocytic thyroiditis; (2) to determine the T-cell stimulatory capability of such isolated thyroid DCs and to compare this capability to that of BB-DP thyrocytes and splenic DCs; and (3) to investigate the phenotype of isolated thyroid DCs and to compare it to that of splenic DCs; and (4) to investigate the capability of such thyroid DCs to regulate thyrocyte growth and function, and to compare it to our earlier reports demonstrating such capability with splenic DCs.Leukokcytic cell fractions were isolated from the thyroids of BB-DP and control Wistar rats of 7-20 weeks of age. The isolation steps included gentle enzymatic tissue disruption, the collection of non-plastic adherent cells and density gradient centrifugation of these cells to yield a low and a high density non-adherent fraction.The low density cell (LDC) fraction was composed of 50-75% leukocytes in both strains. These leukocytes were almost exclusively ED1+ monocytes or MHC-class II+ DC. The high density cell (HDC) fractions of both strains were composed of about 70% MHC-class II-negative thyrocytes and 30% ED1+ monocytes. The thyroid LDCs of both strains had an APC capability in syngeneic(syn)-MLR comparable to that of splenic DCs. However, the HDCs were extremely poor in syngeneic T cell stimulation. There was a difference in composition between the Wistar and the BB-DP LDC fractions: The Wistar LDCs were composed of 30-35% ED1+ monocytes and 15-20% typical MHC-II+ DCs, while BB-DP LDC fractions contained more ED1+ monocytes (about 70%), but fewer DCs (5-10%). In comparison to splenic DCs, thyroid DCs had a low CD80 and CD86 expression in both strains (i.e., an 'immature' phenotype). The LDCs of both animal strains were shown to decrease both basal and TSH-stimulated thyrocyte proliferation and T(3)release by about half.This report shows that a cell fraction enriched for monocytes and DCs can be isolated from the thyroids of both Wistar and BB-DP rats. The cells in this fraction were as capable as splenic DCs to act as T cell stimulators in syn-MLR. Since the thyroid HDCs (predominantly thyrocytes) were very poor at such T cell stimulation, thyroid monocytes and DCs (and not thyrocytes) are the prime candidates to act as immune accessory cells in the initiation of thyroid autoimmunity in the rat. Wistar thyroid LDCs differed in phenotype from BB-DP LDCs. The latter contained a lower percentage of DCs and a higher percentage of their precursors, the monocytes. Interestingly, a defect in the transition of monocytes to DCs has been described in another animal model of autoimmune thyroiditis/insulitis (the NOD mouse), as well as in thyroiditis and diabetic patients.     

Maturation of dendritic cells by necrotic thyrocytes facilitates induction of experimental autoimmune thyroiditis

Dendritic cell (DC) maturation is required for efficient presentation of autoantigens leading to autoimmunity. In this report, we have examined whether release of tissue antigens from necrotic thyroid epithelial cells can trigger DC maturation and initiation of a primary anti-self response. DC were cocultured with either viable (VT/DC) or necrotic (NT/DC) thyrocytes, and their phenotypic and functional maturation as well as immunopathogenic potential were assessed. Significant up-regulation of surface MHC class II and costimulatory molecule expression was observed in NT/DC but not in VT/DC. This was correlated with a functional maturation of NT/DC, determined by IL-12 secretion. Challenge of CBA/J mice with NT/DC, but not with VT/DC, elicited thyroglobulin (Tg)-specific IgG as well as Tg-specific CD4(+) T-cell responses and led to development of experimental autoimmune thyroiditis. These results support the view that thyroid epithelial cell necrosis may cause autoimmune thyroiditis via maturation of intrathyroidal DC.     

Failure of correlation between B7 expression and activation of interleukin-2-secreting T cells

It is well established that triggering interleukin-2 (IL-2) secretion by helper T cells requires the T cell to receive at least two discrete signals. One signal is transduced by the CD3 complex, usually as the result of T cell receptor (TcR) occupancy, the second, or co-stimulatory, signal involves a non-cognate interaction between cell surface accessory molecules on the antigen-presenting cell (APC) and the T cell. A molecular interaction that has been implicated in the provision of co-stimulatory signals is that between B7/BB1 on the APC and its ligands, CD28 and CTL-A4 on the T cell. We have studied the ability of HLA-class II antigen-positive human T cells and a population of DR1-expressing transfected human fibroblasts to stimulate a proliferative response by human T cell clones, and by freshly isolated peripheral blood T cells. Despite their high levels of B7 expression, the T cell clones, were unable to induce proliferation or IL-2 secretion by DR-restricted, antigen-specific T cells. In contrast, the DR1-expressing transfectants, that were B7 negative, induced a strong proliferative response. When these two populations of DR-expressing cells were used to stimulate a primary alloresponse the results were reversed, in that the T cell clones induced a strong alloresponse but the transfected fibroblasts induced no proliferation. These results suggest that the expression of B7 may be necessary for co-stimulation of unprimed T cells, but not of established T cell clones. Furthermore the data show that the expression of B7 by an APC does not necessarily lead to IL-2 production or protection from the induction of tolerance. The mechanisms responsible for the inability of these T cells to provide full activation signals when used as APC is currently under investigation.     

The role of human alveolar macrophages in the allogeneic and autologous mixed leucocyte reactions.

Human alveolar macrophages (AM) are deficient in their ability to promote antigen-stimulated lymphocyte proliferation when compared to in-vitro-aged blood derived macrophages (BM). The mechanisms behind the unique accessory cell function of human AM are unknown. The current paradigm for accessory cell function requires antigen presentation in the context of gene products of the HLA-DR locus of the major histocompatibility complex (Class II, DR antigens) and secretion of non-specific second signal (e.g. interleukin 1). While both AM and in-vitro-aged BM have limited ability to secrete interleukin 1 (IL-1), more than 90% of both cell types express DR antigens. However, only BM consistently promote antigen-stimulated lymphocyte proliferation. Addition of IL-1 does not restore accessory cell function of human AM for antigen stimulation. It is possible that DR antigen expression and/or function of AM may be more contributory for their accessory cell function. The mixed leucocyte reaction (MLR) and autologous mixed leucocyte reactions (AMLR) in which DR epitopes stimulate proliferation of allogeneic and autologous T cells, respectively, are useful in vitro assays for assessment of DR-restricted macrophage-lymphocyte interactions. In the current studies we demonstrate that AM are usually equivalent to autologous in-vitro-aged BM in their ability to stimulate an MLR, but are consistently deficient relative to such BM in their ability to stimulate an AMLR. Experiments in which the two cells were co-cultured indicate that AM-mediated suppression does not account for the limited ability of AM to stimulate an AMLR. The deficiency of AM to act as accessory cells for antigen-stimulated lymphocyte proliferation may relate to their relative inability to stimulate autoreactive T cells and be attributable to differences in DR antigen expression and/or function.     

Intrathyroidal HLA-DR-positive lymphocytes in Hashimoto's disease: increases in CD8 and Leu7 cells

The peripheral and intrathyroidal HLA-DR-positive (DR+) lymphocyte subsets that were activated in vivo in patients with Hashimoto's disease (HD) were examined by two-color flow cytometry with monoclonal antibodies against CD3, CD4, CD8, Leu7, CD19, and HLA-DR antigens. The proportions of total DR+ cells in peripheral lymphocytes and the proportions of DR+ cells in the CD3+, CD4+, and Leu7+ lymphocytes were higher in patients with HD than in normal controls. Furthermore, the proportions of total DR+ cells among intrathyroidal lymphocytes isolated from thyroid tissue of individuals with HD were higher than those in their peripheral lymphocytes. Interestingly, the proportions of DR+ cells among the CD3+, CD8+, and Leu7+ lymphocytes in the thyroid were greatly increased. These data indicate that (i) CD3+ T, especially CD4+ T helper/inducer, lymphocytes and Leu7+ NK/K cells are activated in peripheral blood in Hashimoto's disease and that (ii) CD3+ T, especially CD8+ T suppressor/cytotoxic, lymphocytes and Leu7+ NK/K cells are predominantly activated in Hashimoto's goiter, suggesting an increase of cell-mediated cytotoxicity in the thyroid in Hashimoto's disease.     

Discordant Expression of Ii and HLA-DR in Thyrocytes: A Possible Pathogenetic Factor in Hashimoto's Thyroiditis

Hashimoto’s thyroiditis is the archetype of organ-specific autoimmune disease. The key pathogenetic feature is the activation of thyroid-specific T-cells by properly presented endogenous thyroid antigens. There is strong indication that thyrocytes themselves present self-antigens, based on the finding of antigen presenting human leukocyte antigen-DR (HLA-DR) molecules on the thyrocytes in Hashimoto’s thyroiditis. Because class II-associated invariant chain (li) is tightly bound to the antigen-binding groove of the DR molecules in the endoplasmic reticulum and is found to compete with the endogenous peptides for binding with DR, it is speculated that li prevents endogenous peptides from binding to, and being presented by, DR on the cell surface. We hypothesize that in Hashimoto’s thyroiditis, Ii is insufficient, leaving DR molecules open for endogenous peptides. In this article, we test our hypothesis of discordance between DR and li in the thyroid epithelial cells in Hashimoto’s thyroiditis by immunohistochemistry. Formalin-fixed, paraffin-embedded archival tissue from eight cases of Hashimoto’s thyroiditis and four cases of normal thyroid specimen were randomly selected and immunostained with monoclonal antibodies (MAbs) against HLA-DR and li using avidin-biotin-peroxidase method. We found that in all eight cases of Hashimoto’s thyroiditis, li is significantly reduced relative to DR. The results support our hypothesis that presentation of self-antigen may be a result of insufficient li in the thyrocytes in Hashimoto’s thyroiditis.     

Antigen presentation by interferon-γ-treated thyroid follicular cells inhibits interleukin-2 (IL-2) and supports IL-4 production by B7-dependent human T cells

The consequence of recognition of antigen on antigen-presenting cells that are induced to express major histocompatibility complex (MHC) class II molecules following an inflammatory process is still not clear. In this study, we have investigated the outcome of antigen presentation by epithelial cells and we have used as a model thyroid follicular cells (TFC) that are known to express MHC class II molecules in autoimmune thyroid diseases and acquire the capacity to present autoantigens to T cells infiltrating the thyroid gland. The result show that MHC class II-expressing TFC were unable to stimulate a primary T cell alloresponse, using CD4⁺ T cells from three HLA-mismatched responders. Phenotypic analysis showed that TFC, after incubation with interferon-γ, do not express the co-stimulatory molecules B7-1 (CD80) and -2 (CD86). Addition of murine DAP.3 cells expressing human B7-1 (DAP.3-B7) to cultures containing peripheral blood CD4⁺ T cells and DR1-expressing TFC led to a proliferative response, suggesting that the failure of TFC to stimulate a primary alloresponse was due to a lack of co-stimulation. Similarly, HLA-DR-restricted, influenza-specific T cell clones dependent on B7 for co-stimulation did not respond to peptide presented by TFC; again the lack of response could be overcome by co-culture of TFC with DAP.3-B7. Furthermore, recognition of antigen on TFC inhibited interleukin-2 (IL-2) production in the B7-dependent T cells. In contrast, in T helper type 0 (Th0) T cells, IL-4 release was not affected by TFC presentation. In addition, antigen presentation by TFC favored IL-4 production relative to IL-2 production by B7-indpendent Th0 clones. These results suggest that antigen presentation by MHC class II⁺ TFC may induce tolerance in autoreactive Th1 cells but may simultaneously favors a Th2 response in uncommitted T cells, and thereby support autoantibody production.     

Activation antigens on colonic T cells in inflammatory bowel disease: effects of IL-10

Activated T cells that express activation antigens are termed nonprofessional antigen‐presenting cells (T‐APCs). This study evaluates the ability of lamina propria lymphocytes (LPLs) in inflammatory bowel disease (IBD) to become T‐APCs. LPLs were stained by two‐colour immunofluorescence to determine the expression of activation antigens on T cells. Those from actively inflamed IBD mucosa expressed greater amounts of MHC class II (DR) and CD86 than did LPL T cells from disease controls or normal individuals. After culture in IL‐2 with or without IL‐10, the ability of the T‐APCs from IBD colon to stimulate allogeneic peripheral blood T cell proliferation was measured. The T‐APCs from IBD stimulated an allogeneic mixed lymphocyte reaction, particularly through their expression of DR and CD86, as demonstrated by antibody blocking. Normal LPLs acquired these properties only if repeatedly stimulated with allogeneic peripheral blood lymphocytes (PBLs) used as cell lines in the presence of IL‐2. Addition of IL‐10 reduced expression of activation antigens and the stimulatory ability of LPLs from either IBD patients or from these cell lines. In summary, LPLs from active IBD, but not from disease controls, express activation antigens that stimulate naïve T cells, a process that is reduced by IL‐10. This may contribute to perpetuation of the inflammation.     

Methimazole blocks Graves' IgG but not interferon-gamma HLA-DR expression by thyroid cells

We have expanded our early observation that a potent Graves' IgG preparation induces HLA-DR expression on thyroid cells, by showing that four randomly-selected Graves' IgG's were also capable of inducing DR antigens on thyroid cells. The effect of Graves' IgG was specific to thyroid cells, as it did not induce MHC Class II molecule expression on endothelial cells whereas interferon-gamma and immune complexes did so. The anti-thyroid drug methimazole was capable of rapidly reducing Graves' IgG-induced DR expression but to a much lesser extent than brought about by interferon-gamma. We conclude that Graves' IgG propagates thyroid-specific autoaggression by continued induction of DR antigens and than an important means whereby methimazole brings about remission is by reducing this induction.     

Interleukin-18 synthesis and secretion by dendritic cells are modulated by interaction with antigen-specific T cells.

We show that interleukin-18 is constitutively produced by dendritic cells; synthesis and secretion are poorly affected by maturative stimuli. Challenge of dendritic cells with autologous anti-tetanus toxoid T lymphocytes results in a secretory switch, with induction of secretion of biologically active interleukin-18 and decrease of its intracellular content. Similarly, when dendritic cells are challenged with allospecific T cells a dramatic decrease of intracellular interleukin-18 content occurs, whereas no effects are observed after co-culture with autologous activated T cells. The induction of secretion call be mediated by engagement of CD40 on dendritic cells, as indicated by the increased amount of interleukin-18 in dendritic cell supernatants after CD40 triggering by anti-CD40 antibodies. However, CD40 engagement, unlike from antigen-specific T cells, does not result in reduced intracellular interleukin-18 content, suggesting that this decrease may be mediated by structure(s) involved in antigen recognition.     

Induction of intercellular adhesion molecule-1 but not of lymphocyte function-associated antigen-3 in thyroid follicular cells.

We investigated the expression of intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-3 (LFA-3) by thyrocytes and their regulation by cytokines. Immunofluorescence studies on cryostat sections and on freshly dispersed cell preparations showed that ICAM-1 and LFA-3 are barely detectable in non-autoimmune thyrocytes. However, thyrocytes acquired ICAM-1 expression in culture. IFN-gamma, IL-1 beta and TNF-alpha produced a clear enhancement of ICAM-1 expression. When tested in combination, IL-1 beta and TNF-alpha were additive to the IFN-gamma effect. LFA-3 expression was not modulated by these cytokines. In the HT93 thyroid cell line generated by transfection with SV40, ICAM-1 and LFA-3 were both constitutively expressed at high levels. Cytokines modulated ICAM-1 expression similarly, but to a greater extent than in normal thyrocytes. LFA-3 remained unmodified. These results support the notion that normal thyrocytes are immunologically silent cells. The capability of cytokines to induce ICAM-1 together with HLA class I and class II-expression on thyrocytes suggests that under their influence, these cells may express all the surface molecules required for antigen presentation and/or for being recognized as target cells in the context of thyroid autoimmune disease.     

Engagement of CD40 lowers the threshold for activation of resting B cells via antigen receptor

Cross-linking of surface Ig (sIg) on resting B cells can generate intracellular signals; however, for T-dependent antigens to promote growth and differentiation additional surface receptors must be engaged. Ligation of CD40 can stimulate B cell proliferation in the presence of interleukin-4. A recently identified counterstructure for CD40 is found on T helper cells and is believed to represent the cognate ligand for B cell activation. This study investigates the role of CD40 as an accessory molecule in sIg-dependent B cell activation. Simultaneous ligation of sIg and CD40 by monoclonal antibodies (mAb) in the presence of mouse L cells which express human Fey receptor type II (FcγRII-L cells) results in potent stimulation of small resting B cells. When CD40 is co-ligated, picomolar concentrations of mouse IgG1 anti-μ, and anti-δ mAb can stimulate B cell proliferation. This requires interaction of the anti-Ig mAb with the FcγRII-L cells: a mouse IgG2a anti-μ, mAb which is not recognized by FcγRII, was ≥ 1000-fold less effective. These findings suggest a mechanism for B cell activation whereby engagement of T cells via CD40 and its cognate ligand provides potent enhancement of signals delivered through sIg. Based on these observations, models for the activation of B cells by T-dependent antigens are presented.     

Effective antigen presentation to helper T cells by human eosinophils

Although eosinophils are inflammatory cells, there is increasing attention on their immunomodulatory roles. For example, murine eosinophils can present antigen to CD4⁺ T helper (Th) cells, but it remains unclear whether human eosinophils also have this ability. This study determined whether human eosinophils present a range of antigens, including allergens, to activate Th cells, and characterized their expression of MHC class II and co‐stimulatory molecules required for effective presentation. Human peripheral blood eosinophils purified from non‐allergic donors were pulsed with the antigens house dust mite extract (HDM), Timothy Grass extract (TG) or Mycobacterium tuberculosis purified protein derivative (PPD), before co‐culture with autologous CD4⁺ Th cells. Proliferative and cytokine responses were measured, with eosinophil expression of HLA‐DR/DP/DQ and the co‐stimulatory molecules CD40, CD80 and CD86 determined by flow cytometry. Eosinophils pulsed with HDM, TG or PPD drove Th cell proliferation, with the response strength dependent on antigen concentration. The cytokine responses varied with donor and antigen, and were not biased towards any particular Th subset, often including combinations of pro‐ and anti‐inflammatory cytokines. Eosinophils up‐regulated surface expression of HLA‐DR/DP/DQ, CD80, CD86 and CD40 in culture, increases that were sustained over 5 days when incubated with antigens, including HDM, or the major allergens it contains, Der p I or Der p II. Human eosinophils can, therefore, act as effective antigen‐presenting cells to stimulate varied Th cell responses against a panel of antigens including HDM, TG or PPD, an ability that may help to determine the development of allergic disease.