Inhibiton of the colony-forming capacity of human T-lymphocytes exerted by theophylline

The effects of theophylline on T-lymphocyte colony formation were investigated both by in vitro studies (adding theophylline in cultures at three different concentrations--5, 15 and 30 micrograms/ml) and by in vivo experiments (after oral ingestion of 10 mg/kg time-released theophylline) in a group of young healthy volunteers. In vitro the drug showed a significant dose-dependent inhibitory effect on both peripheral mononuclear cells (PMNC) and purified T-lymphocyte colony formation. No significant differences in PMNC colony formation before and 12 h after the oral ingestion of theophylline was detected in the in vivo study, even if at the same time the plasma concentration of the drug remained at therapeutic level in every subject. In addition, in vitro experiments mimicking the in vivo conditions suggested that the apparent disagreement between the in vitro and in vivo results was due to experimental procedures (i.e. the inhibitory effect requires the constant presence of the theophylline in the culture medium). The experimental data provided in this study confirm, using different experimental procedures, the results of our recent investigations showing that theophylline exerts an inhibitory effect on T-cell proliferation.

T cell activation through different membrane structures (T3/Ti, T11, T44) and frequency analysis of proliferating and interleukin-2 producer T lymphocyte precursors in aged individuals

It is well known that the proliferative responsiveness of T cells of aged subjects is depressed in both autologous mixed lymphocyte reaction (AMLR) and in PHA-induced cultures. In the present study we analyzed T cell activation through different stimulatory pathways (such as T3/Ti antigen receptor, T11 complex and T44 molecule). Moreover, we studied Interleukin-2 (IL-2) release performing a limiting dilution analysis of the proliferative capability of peripheral blood T cells, employing a high efficiency cloning technique. Our results demonstrate normal proliferation of T3-induced T cells in aged subjects, whereas T11- and T44-induced T cell proliferations are depressed in aged subjects. In addition, studies at clonal level reveal a normal percentage of IL-2 producer T cell in aged individuals. In conclusion, our data suggest that the T cell in aged subjects are normal in number, but they have a decreased capacity of lymphokine production.

Fenoterol effects on the in vitro immune response

Beta-2-adrenergic agonists are often employed in the treatment of acute bronchostenosis. Following our recent investigations into the influence of some drugs (cromolyn, ketotifen, theophylline) on the immune response, in this study we analyzed the in vitro effects of fenoterol (beta-2-adrenergic agonist) on the immune response. The mitogen-(PHA)-induced proliferation of peripheral mononuclear cells (PMNC), the PMNC proliferation induced by anti-T3 and anti-T11 monoclonal antibodies (MAbs), the PHA-induced lymphokine--interleukin 2 (IL-2) and interferon-gamma (IFN-gamma)--production were studied in ten healthy volunteers. Since the plasmatic peak of fenoterol following a single inhalation of 200 micrograms is about 20 ng/ml, in the experiments herein reported the drug was tested in the cultures at concentrations lower, equal and higher than the plasmatic peak: respectively, 2, 20 and 200 ng/ml. Furthermore, for a more detailed study of T-lymphocyte activities, we also evaluated the effect of fenoterol on T-cell clone proliferation. Our results, which reveal no effects of fenoterol on the studied immunological parameters, acquire relevance when related to our previous reports showing a depression of the immunological response exerted by theophylline and ketotifen.

Terfenadine (single or associated) treatment of adverse reactions to foods

Six groups of patients (total 105), affected by cutaneous signs and symptoms related to food ingestion were studied with regards to the clinical efficacy of some pharmacologic treatments: blind placebo, terfenadine alone, terfenadine associated with pirenzepine or rosaprostol or ranitidine or famotidine. Pharmacologic treatment by terfenadine alone showed poor clinical results, similar to placebo, while the associations of terfenadine with both cytoprotective drugs and anti-H2 receptor antagonists revealed significant clinical improvement which is more evident in those patients treated with cytoprotective drugs combination than those who were treated with anti-H2 antagonists.

Glycoproteic nature of surface molecules of effector cells with lymphokine-activated killer (LAK) activity. Evidence that T11, T8 or T3 molecules are not involved in tumor-cell lysis by LAK effector T cells

Human peripheral blood mononuclear cells cultured in the presence of interleukin-2 (IL-2) acquire the capability of lysing NK-resistant fresh tumor target cells. In an attempt to delineate the surface structure(s) present on the effector cells, the latter were first treated with different amounts of pronase and neuraminidase. The effect of the enzymes on cytolytic activity against fresh melanoma cells was evaluated and compared with the NK-like activity against K562 target cells of the same effector population. At a pronase concentration of 0.01 mg/ml, no inhibition of NK-like activity was detected, whereas LAK activity was inhibited by more than 75%. In addition, neuraminidase had no effect on NK-like activity, even at 1 U/ml, whereas as little as 0.03 U/ml inhibited LAK activity by more than 75%. Metabolic inhibition of N-linked glycosylation with Tunicamycin prevented the generation of LAK activity, even when added late (18 hr before termination of the culture). Tunicamycin, on the other hand, had no effect on the boost of NK activity induced by IL-2. Provided that LAK activity can also be generated in T-cell (E-rosetting) populations, in the presence of adherent cells, we analyzed the inhibitory activity of monoclonal antibodies (MAbs) to T11, T3 and T8 molecules. While all these MAbs strongly inhibited the specific target cell lysis by alloreactive CTLs, they had no effect on the LAK activity.

Alpha 1-acid glycoprotein (alpha 1-AGP) on the membrane of human lymphocytes: possible involvement in cellular activation

A glycoprotein termed alpha 1-acid glycoprotein (alpha 1-AGP) is a component of normal human serum; its concentration is often increased in several pathological disorders, including acute inflammation and cancer. Inhibitory effects of alpha 1-AGP on some in vitro T and B cell function assays have been reported but our recent data indicated that alpha 1-AGP is indeed a T cell mitogen at physiological concentrations. The present study was designed to investigate: (a) the relationship between this glycoprotein and two other glycoproteins of the T and B cell membrane, i.e. the T3 and Ia antigens; (b) the ability of lymphocytes to take up exogenous alpha 1-AGP; (c) the different expression of alpha 1-AGP on the T cell membrane upon different activation pathways, i.e., autologous non-T-cells (B cells and monocytes) phytohemagglutinin and anti-T3 monoclonal antibody (MAb) stimulations. The data reported herein show no competition at the membrane level between anti-alpha 1-AGP and anti-T3 or anti-Ia MAbs. In addition, (1) the lymphocytes were able to absorb alpha 1-AGP from the culture medium and (2) the expression of this glycoprotein was enhanced upon T cell stimulation (all three stimulants employed induced an increase of alpha 1-AGP positive T cells), thus suggesting a possible role of this glycoprotein in in vitro T cell activation.

Pharmacologic treatment of adverse reactions to foods: comparison of different protocols

The authors evaluated four different therapeutic protocols employing 80 adult patients with clinical symptoms (urticaria and/or angioedema) due to food ingestion. Thirty-seven patients were allergic. In these cases the diagnosis was made on the basis of simultaneous positivity of the following criteria: history, exclusion diet and challenge tests, positive prick tests, and a positive PRIST and RAST. The other 43 subjects were considered to have pseudo-allergic reactions (PSAR). The pharmacologic treatment was performed for 4 to 6 weeks and each patient had a free diet during the study. At the end of the treatment, both the patient and the allergist filled a score questionnaire concerning the clinical status in order to evaluate the clinical improvement. Our data indicate that anti-H1 antihistamines do not significantly differ from placebos, that oral cromolyn is more successful in food allergy than in PSAR patients (P less than .05), that ketotifen is helpful, and that the association of H1 and H2 anti-histamine drugs is even more effective. Finally, by considering the effect on the immune system exerted by these drugs, as recently demonstrated in our laboratory, a detailed balance of each therapeutic protocol is then analyzed.

Occurrence of lymphocyte proliferative response to thyroglobulin and antithyroglobulin antibodies in normal individuals: lack of correlation with HLA

Peripheral mononuclear cells (MNC) of patients with autoimmune thyroid disease have been shown to proliferate when cultured with human thyroglobulin (hTg). In addition, such a phenomenon is apparent in a certain number of healthy individuals. In this study we have attempted to correlate hTg-induced MNC proliferation, occurrence of anti-hTg autoantibodies and HLA phenotype (including Class II DR and DQ loci) in a population of HLA-typed normal blood donors. Fourteen out of 56 subjects showed a significant MNC proliferation to hTg. Three of them had anti-hTg autoantibodies in the serum, while none of the hTg-unresponsive subjects showed such antibodies. No correlation with HLA phenotype (including Class II DR5 specificity, referred as associated with Hashimoto's thyroiditis, and DQ alleles) was observed.

Alterations in helper-specific circulating T lymphocytes and in the autologous mixed lymphocyte reaction in chronic hepatitis B

Defects in T lymphocyte subpopulations and in the functional characteristics of such cells have been thought to play a role in the evolution of chronic hepatitis B, but the precise nature of the alterations and their significance remains unresolved. We studied lymphocyte subsets in 27 patients with chronic hepatitis B utilizing standard monoclonal antibodies including Leu 1,2a,3a,7 and D1/12 (against the common determinant of the Dr molecule), as well as a newly described monoclonal antibody, "5/9," which is thought to characterize a unique subpopulation of T4 cells with specific helper/inducer function. These results were compared with those obtained using the autologous mixed lymphocyte reaction assay for the same patients in order to further delineate the lymphocyte alterations in chronic hepatitis B. A significant reduction in the mean number of Leu 3a (T4) positive cells was observed as well as a reduction in the number of 5/9 positive cells. These changes were most evident in those positive for HBeAg in serum. Reduction in Leu 3a cells was associated with a reduced autologous mixed lymphocyte reaction assay response, and was most marked in the HBeAg-positive individuals. These findings suggest that HBeAg-positive patients in whom active viral replication is occurring have a defect in T lymphocyte number and function, which may be due in part to reduced 5/9 positive cells. These alterations may be related to the persistence of virus in chronic active hepatitis B patients.

Clonal analysis of T lymphocytes infiltrating the thyroid gland in Hashimoto's thyroiditis

T cells isolated from thyroid tissue and peripheral blood of 2 patients with Hashimoto's thyroiditis were studied by a high cloning efficiency microculture technique. Clonal efficiencies of 37 and 24% were obtained from thyroid-derived T cell cultures, while 40 and 90% efficiencies resulted from peripheral-blood-derived cultures. A prevalence of T4-/T8+ T cell clones were found in thyroid infiltrates. The functional analysis of the clones demonstrated significantly higher proportions of clones with cytolytic activity in a lectin-dependent assay in thyroid-derived microcultures, as compared to peripheral blood-derived ones. The proportion of clones displaying natural-killer-like activity was increased in 1 patient only. Cytolytic activity was displayed not only by all T4-/T8+, but also by several T4+/T8- intrathyroid clones. Remarkable proportions of cytolytic clones were also able to release interleukin-2 upon phytohemagglutinin stimulation. Finally, the proportion of T cell clones able to release gamma-interferon following mitogen stimulation was significantly higher in thyroid- vs. peripheral-blood-derived microcultures. These results provide further data about the possible pathogenetical role of both regulatory and effector T lymphocytes in human autoimmune thyroiditis.

T cell activation surface markers and autologous mixed lymphocyte reaction do not differ in true and pseudo food allergy

Eighteen patients affected by itching, urticaria, eczema, angioedema, and asthma related to food-stuff intake were studied and classified in two groups (true food allergy and pseudoallergy) on the basis of clinical data, skin prick tests, total and specific IgE levels (PRIST and RAST) and double-blind challenge test. Autologous mixed lymphocyte reaction (AMLR) and T cell activation markers were thought to be tests possibly useful to discriminate between 'true' food allergy and 'pseudoallergy'. The present study failed to show either a significant increase in T cell activation markers (MLR4, Ia) or a significant decrease in AMLR proliferation in such subjects as compared to normal controls. In addition, we found no differences between 'true' allergic and 'pseudoallergic' patients on the basis of the parameters evaluated. Although the AMLR defect was reported both in asthma and in dermatitis, and therefore was thought to be related to atopy, the present data do not confirm this hypothesis in 'true' food allergy.

In vitro effects of Bacillus subtilis on the immune response

The authors evaluated the in vitro effects of Bacillus subtilis on the following parameters of the immune response: mitogenic T cell proliferation (by PHA and OKT3) and mitogenic-induced lymphokine production (IL-2 and IFN-gamma). The spores of Bacillus subtilis did not influence the immune response, while its vegetative forms enhanced mitogenic-induced T cell proliferation. Both spores and vegetative forms did not modify lymphokine production.

Effects of an adjunctive treatment with Bacillus subtilis for food allergy

The authors evaluated the clinical efficacy of an adjunctive treatment with spores of Bacillus subtilis in 20 adult patients with urticaria-angioedema syndrome from food allergy. The patients treated with B. subtilis showed a significant reduction in frequency and severity of clinical features in respect to the patients who received no treatment. Bacillus subtilis spores may increase S-IgA synthesis or protect gastroenteric mucosa.

Does normal lymphocyte DNA synthesis in response to PHA exclude cell-mediated immunodepression?

PHA stimulation assay was the first in vitro method for evaluating the T-cell function, and this T-cell proliferative response has been routinely used to discriminate between normal subjects and patients with deficiency in cell-mediated immunity. However, [3H]thymidine incorporation into lymphocyte DNA can be studied by using additional in vitro assay methods since they measure different lymphocyte activation pathways. In the present study we selected three different tests to investigate the reliability of this single approach: PHA induced lymphocyte DNA synthesis; T lymphocyte DNA synthesis to anti-T3 monoclonal antibody (OKT3); autologous mixed lymphocyte reaction (AMLR). In addition, IL-2 receptor expression on the membrane of T-cell stimulated in AMLR both with PHA and anti-T3 was evaluated. This study was performed in various groups of subjects: normal young controls, aged healthy individuals, and patients with Alzheimer's disease (AD), Retinitis Pigmentosa (RP), and with cell-mediated immunodeficiency and clinical evidence of recurrent viral infections (ID). The data reported herein show heterogeneity of results in each group studied and demonstrate the necessity of employing more than one laboratory test for the routine evaluation of T-cell-mediated immunity.

Inhibitory effect of an antibody against alpha 1-acid glycoprotein (alpha 1-AGP) on autologous mixed lymphocyte reaction and anti-T3 T-lymphocyte activation

The action of an anti-alpha 1-AGP antibody on AMLR, anti-T3 and PHA T-lymphocyte proliferative response was evaluated. We observed a strong dose-dependent inhibition on T-lymphocyte proliferative responsiveness to autologous non-T cells and to anti-T3 stimulus, whereas PHA activation was unaffected. A lower degree of inhibition of the proliferative response was also observed on pretreating both T and non-T cells with the antibody; the addition of anti-alpha 1-AGP in the culture containing cells pretreated with the antibody showed a further inhibition of thymidine incorporation. The data suggest a direct influence of the antibody on membrane alpha 1-AGP and support a positive role of this glycoprotein (distinct from Ia and T3 antigens) on both anti-T3 and autologous non-T cell T-lymphocyte responsiveness, thus indicating the involvement of alpha 1-AGP in the T3-Ti antigen-specific pathway of T-cell activation.

Oral cromolyn in food allergy: in vivo and in vitro effects

The results obtained in vivo in a group of 24 patients treated with oral cromolyn and compared to a group of 10 patients treated with placebo are reported. All patients were affected by adverse clinical reactions (urticaria and/or angioedema) related to food ingestion. A significant reduction of signs and symptoms were observed after oral cromolyn therapy only in the patients affected by true food allergy (FA), i.e., IgE mediated reactions. No adverse reactions appeared in the treated patients. Because we found an enhancing effect exerted in vitro by cromolyn (SCG) on T-cell responsiveness in previous studies, in the present investigation we analyzed in more detail in vitro effects of SCG on T lymphocytes [i.e., phytohemagglutinin-induced interleukin-2 (IL-2) production] and IL-2 receptor expression on T cells. No significant effect was induced by SCG on IL-2 production, whereas IL-2 receptor expression on surface of T cells appeared significantly increased (P less than 0.001) by adding SCG in cultures. These clinical and immunological results are analyzed and discussed in relation to a possible in vivo effect(s) of cromolyn in allergic diseases.

Inhibition of T3 mediated T-cell proliferation by Ca2+-channel blockers and inhibitors of Ca2+/phospholipid-dependent kinase

The potential roles of Ca2+ ions in the response of T lymphocytes to stimulation with monoclonal antisera to the T3 antigen were investigated by means of pharmacological agents that predominantly inhibit the flux of Ca2+ ions into cells (verapamil, nifedipine) or the activity of Ca2+-dependent kinases (trifluoperazine, polymyxin B). As assessed by uptake of [3H]thymidine, proliferation induced with anti-T3 +/- recombinant IL-2 at 72 h was inhibited by greater than 80% in the presence of nifedipine at 50 microM, and almost completely arrested (greater than 95% inhibition) with the other agents at the same concentration. Further quantitative assays of the effects of polymyxin B and trifluoperazine on C-kinase labelling of exogenous substrate showed a major reduction with both agents, but inhibition was substantially greater with polymyxin B that with trifluoperazine (IC50 = 14 and 70 microM respectively). These results were confirmed by qualitative assessment of Ca2+/phospholipid-dependent phosphorylation of endogenous substrates, which demonstrated major phosphoproteins of MW 56,000, 52,000, 43,000, and 20,000, and dose-dependent reduction in labelling in the presence of polymyxin B. Similar results were obtained under more physiological conditions in intact cells labelled with 32P orthophosphate. These findings indicate several possible roles for Ca2+ in T-cell activation, and several possible levels of activity, including modulation of calmodulin-dependent kinases and effects on Ca2+/phospholipid-dependent kinases and Ca2+ channels.

T lymphocyte subsets implicated in cytotoxicity in autologous hepatocytes in chronic active hepatitis patients with active viral replication

We investigated inhibitory effect of various monoclonal antibodies on T-cell-mediated cytotoxicity against autologous hepatocytes in 24 patients with hepatitis B surface antigen/hepatitis B e antigen (HBsAg/HBeAg)-positive chronic active hepatitis. A significant reduction of cytotoxicity index occurred after preincubation of T lymphocytes with anti-Leu 7 (killer-natural killer cells), D1/12 (Ia-positive cells), 5/9 (restricted helper/inducer cells), and MLR4 ("activated" and radiosensitive helper cells) monoclonal antibodies (MAb). Anti-Leu 2a (cytotoxic/suppressor cells) and anti-Leu 3a (helper/inducer cells) MAb did not affect cytotoxic activity. This finding supports the hypothesis that the T cytotoxic reaction in this in vitro system is probably due to two mechanisms: first, spontaneous cell membrane cytotoxicity sustained by anti-Leu-7-positive lymphocytes; and second, specific cytotoxicity mediated by activated Ia-positive cells. We also found that the presence of helper/inducer cells (5/9 positive) appears to be a prerequisite for the cytotoxic reaction.

Evidence of T-lymphocyte functional impairment in Huntington's disease

Huntington's Disease (HD) is a degenerative neurological disorder with autosomal dominant transmission. Although immunological defect(s) have been postulated, no confirmed laboratory evidence for this exists. In the present study we observed activated T cells in the peripheral blood of HD patients (using 4F2 monoclonal antibody), whereas the percentage of T cells bearing T-cell activation markers such as HLA-DR and MLR4 antigens was normal. We then studied T cells of HD patients in some functional assays. Since it has been suggested that autologous mixed lymphocyte reaction (AMLR) includes several immune mechanisms in which distinct cell subsets interact and perform distinct regulatory functions, it is conceivable that the remarkable deficiency of AMLR herein observed in HD patients results from some abnormal immune regulation which may contribute to the pathology of this condition. Additional experiments demonstrated a defect of AMLR in three asymptomatic young sibs of HD patients, and coculture experiments between T cells of patients (as responders) and non-T cells of their sibs (as stimulators), and vice versa, produced no proliferative response. Subnormal responsiveness in allogeneic MLR was also observed. Normal or enhanced PHA-induced production of both IL-2 and IFN-gamma in vitro was detected. These experimental data suggest a cellular branch of the immune system in HD; however, they do not indicate if this defect is primary or secondary to the disease itself.

Functional characterization of a regulatory human T-cell subpopulation increasing during autologous MLR

The present study was undertaken to investigate the heterogeneity of helper T cells in humans using two different monoclonal antibodies: 5/9 and MLR4. The former identifies 15-20% of resting T lymphocytes from peripheral blood and corresponds to an anti-helper/inducer T cell. The second antibody, MLR4, recognizes 5% of total T lymphocytes and partially overlaps with the 5/9+ T cells. In order to investigate functional differences within the 5/9+ cells, we separated two different subsets (5/9+ MLR+ and 5/9+ MLR4-) by a rosetting technique. Although both subsets provide help for Ig synthesis in a PWM-stimulated culture, only the 5/9+ MLR4- fraction gave a proliferative response in both autologous and allogeneic MLR and to soluble protein antigens. The effect of radiation on the ability of the two subsets to provide help for Ig synthesis showed that the 5/9+ MLR4+ subset is highly radiation-sensitive, while 5/9+ MLR- is relatively radiation-resistant. In a further series of experiments, 5/9+ MLR4+ cells isolated after activation in an autologous MLR but not by Con A, were no longer able to induce T-cell differentiation but now showed a strong suppressor effect. The 5/9+ MLR4- subset separated from the same cultures did not display any suppressor function. These data demonstrate in fresh PBL the existence of a radiation-sensitive regulatory subset exerting a helper activity, and which acquires suppressor activity after activation in autologous MLR.

Ketotifen treatment of adverse reactions to foods: clinical and immunological effects

Fifteen patients with cutaneous signs and symptoms caused by adverse reactions to foods were treated in an open trial with ketotifen for 4 to 6 weeks. Seven subjects were allergic and 8 had food intolerance. Each patient was treated with a single dose of ketotifen daily: 2 mg half an hour before going to sleep. Clinical improvement was achieved in 6 out of 7 allergic patients and in 6 out of 8 patients with food intolerance. Since several drugs have been demonstrated to have an influence on immune response, the in vitro effects of ketotifen on some immunological parameters were also studied. Ketotifen showed a significant inhibitory effect on autologous mixed lymphocyte reaction responsiveness.

Autologous mixed lymphocyte reaction in Graves' disease: relationship to clinical status

The autologous mixed lymphocyte reaction (AMLR), i.e. the ability of T lymphocytes to proliferate when cultured with autologous non-T cell fractions, is an 'in vitro' phenomenon showing immunological memory and specificity, probably related to the cooperation ability of immunocompetent cells. We have evaluated AMLR in 27 patients with Graves' disease of varying clinical status (untreated and treated with antithyroid drugs, surgery or 131I). The results obtained show: Impaired AMLR in untreated patients (as in other autoimmune diseases). Significantly higher AMLR in cured patients, and that AMLR in cured patients varies with the treatment (higher after surgery or radioiodine than after medical treatment). These results are consistent with the hypothesis of a functional defect of T cells in Graves' disease, which improves when clinical remission is achieved.

Defect of autologous mixed lymphocyte reaction and interleukin-2 in aged individuals

The proliferative responsiveness of T cells of aged individuals is known to be depressed in both autologous mixed lymphocyte reaction (AMLR) and in PHA-stimulated cultures. In the present study we confirm previous results and also report decreased IL-2 and normal IFN-gamma production (PHA-induced) in aged subjects as compared to young normals. In addition, similar percentages of T lymphocytes expressing surface IL-2 receptors both in the peripheral blood and after different stimulations, i.e. AMLR and PHA, were detected in young and aged individuals. The addition of exogenous IL-2 induces a sharp increase of spontaneous and AMLR proliferation in young individuals, whereas the increase is only slight in aged subjects. The experiments reported herein suggest that in general the T cell proliferation in AMLR is not completely dependent on the presence of IL-2 in the cultures and that aged subjects are probably defective in the production of other factor(s) presumably involved in AMLR proliferation, since the addition of exogenous IL-2 does not produce T-cell proliferation comparable to normal young subjects. The possible meanings of these experimental evidences in AMLR and in the defective immune responses of aged subjects are discussed.

Proliferation of T8-positive cytolytic T lymphocytes in response to thyroglobulin in human autoimmune thyroiditis: analysis of cell interactions and culture requirements

These experiments were designed to analyze the involvement of T-lymphocyte subpopulations in autoimmune thyroid disorders such as Graves' Disease (GD) and Hashimoto's Disease (HD). In a first set of experiments, lymphocytes isolated from thyroid infiltrates or from peripheral blood of GD and HD patients were analyzed for the expression of various surface antigens. While HLA-DR + T cells were numerous among thyroid infiltrating T lymphocytes in both groups of patients, the proportions of T8 + cells (as defined by their reactivity with the B 9.4 monoclonal antibody specific for T8 surface molecule) were strikingly different in HD and GD. In the latter group of patients only 19% of infiltrating T cells were T8 +, whereas these cells represented approximately 50% in four HD patients. Given the previous demonstration that all T cells expressing T8 antigen are cytolytic T lymphocytes (CTL) or their precursors (CTL-P) in conjunction with the fact that lymphocytes from HD or GD patients are known to proliferate in vitro in response to human tg (Htg), we further analyzed the T-cell subset(s) responsible for in vitro proliferation to Htg. In these experiments, peripheral blood T lymphocytes purified from patients with GD or HD were cultured with 1 microgram/ml Htg and irradiated autologous T-depleted mononuclear cells as the source of antigen presenting cells (APC). The proportions of T8 + cells declined considerably during culture in GD patients, but at Days 6 to 9, T8 + cells represented as much as 51% of cultured T lymphocytes from patients with HD. Moreover, the majority of T8 + cells were medium-large size lymphoblasts. Removal of Htg at Day 6 resulted in both abrogation of proliferative responsiveness and in decreases of T8 + percentages. Further analysis of the cell interactions leading to T8 + cell proliferation in response to Htg showed that helper/inducer T cells, as defined by 5/9 antigen expression, were strictly required. Collectively, these features are reminiscent of the T-cell involvement in experimental autoimmune thyroiditis of mice and stress for the first time the potential role of CTL in tissue damage occurring in Hashimoto's thyroiditis.