Cyclosporin A and prednisolone do not inhibit the expression of high-affinity receptors for interleukin 2

To elucidate the mechanisms of action of cyclosporin A (CyA) and prednisolone (pred), we investigated the effects of these immunosuppressive drugs on the expression of receptors for interleukin 2 (IL-2) as well as the effect of exogenous IL-2 on CyA-inhibited and pred-inhibited responses. Pred-induced inhibition of T cell proliferative responses could be reversed by addition of exogenous IL-2. In contrast, exogenous IL-2 could not overcome CyA-mediated inhibition of T cell proliferation. Receptors for IL-2, as measured by the expression of Tac antigen, were slightly decreased by CyA and pred. However, expression of the biologically active, high-affinity IL-2 receptors was not diminished. These data suggest that pred-mediated inhibition occurs at the level of the IL-2 system, whereas CyA affects the proliferative mechanism of the T cell itself

Pharmacodynamic modeling of lymphocytopenia and whole blood lymphocyte cultures in prednisolone-treated individuals

In this study, we describe the time course of the influence of a single oral dose of prednisolone (10 mg) in man on the proliferative response of peripheral blood lymphocytes in whole blood. The data were fitted to an integrated pharmacokinetic-pharmacodynamic model, relating the plasma concentrations of prednisolone to its effect. The determination of prednisolone-induced lymphocytopenia and monocytopenia in vivo and the assessment of the influence of varying lymphocyte and monocyte numbers on proliferative responses in vitro enabled us to calculate the relative contributions of several prednisolone-induced effects to the diminished lymphoproliferative responses in whole blood after administration of prednisolone in vivo. We demonstrate that the decrease of the proliferative response in whole blood lymphocyte cultures stimulated with a monoclonal antibody directed against CD3 is mainly determined by the time course of the prednisolone-induced lymphocytopenia. The time course of the monocytopenia and the relative changes in the CD4+ and CD8+ T-cell subpopulations induced by prednisolone and the direct inhibitory effect of the changing plasma concentrations of the drug also contribute to the decrease of aCD3-stimulated whole blood lymphocyte cultures to some extent. The decrease of the proliferative response in whole blood lymphocyte cultures stimulated with a horse anti-human lymphocyte serum closely followed the time course of the lymphocytopenia induced by prednisolone. However, this response remained decreased for a longer period of time than could be expected on the basis of the prednisolone-induced lymphocytopenia in vivo. A possible mechanism which might explain this discrepancy between the prednisolone-induced effects in vivo and in vitro will be discussed

Prednisolone and cyclosporin a exert differential inhibitory effects on T-cell proliferation in vitro

To elucidate the mechanisms of action of prednisolone (pred) and cyclosporin A (CyA), we have investigated the effects of these immunosuppressive drugs on the proliferative response of human peripheral blood lymphocytes (PBMN) induced by various stimulants, well defined with regard to their monocyte dependence. We found that pred-induced inhibition of monocyte-dependent proliferative responses could be reversed by the addition of exogenous interleukin 2 (IL-2). Monocyte-independent proliferative responses were not affected by pred. These findings suggest that pred inhibits IL-2 production and subsequent lymphocyte proliferation at the level of the signal derived from the monocyte. In contrast, CyA inhibited monocyte-dependent as well as monocyte-independent proliferative responses of human PBMN. This inhibition could not be reversed by the addition of exogenous IL-2. We have previously demonstrated that CyA does not affect the expression of receptors for IL-2. Taken together, these data indicate that CyA-mediated inhibition does not primarily occur at the level of the IL-2 system, but rather affects the proliferative mechanism of the T cell itself. These data clearly demonstrate that pred and CyA act at distinct sites of the triggering process

Low T cell reactivity to combined CD3 plus CD28 stimulation is predictive for progression to AIDS: correlation with decreased CD28 expression

In 219 HIV-1-infected men of the Amsterdam cohort we measured CD4+ T cell numbers and in vitro T cell responses to CD3 MoAbs with or without CD28 costimulation and phytohaemagglutinin (PHA). The value of these markers was estimated for disease progression within 4 years. CD28 expression on T cells has been related to T cell responses. CD28 costimulation considerably enhanced T cell reactivity (≈8–10-fold) with lower coefficients of variation compared with reactivity to CD3 MoAb alone (median 5 versus 20). T cell reactivity to CD3 plus CD28 MoAb was decreased during HIV-1 infection and was besides CD4+ T cell numbers the only independent predictor for progression to AIDS. Compared with the group with high CD4+ T cell numbers the relative risk (RR) for the group with intermediate levels was 2.28, with low levels 5.20. In the groups with intermediate and low CD3 plus CD28 responses the RR was 2.04 and 4.16, respectively. The combined RR for both was 4.65 and 21.63. The independence of this marker was confirmed when the group with low CD4+ T cell numbers was subdivided into groups with high, intermediate and low T cell responses. The expansion of CD8+CD28− T cells was already apparent in HIV− homosexual men, but CD8+CD28+ T cells specifically decreased in patients with AIDS. CD28 expression on T cells correlated moderately with T cell responses to CD3 plus CD28 MoAb. T cell reactivity to CD3 MoAb in the presence of CD28 MoAb is a stronger prognostic marker than T cell reactivity to CD3 MoAb alone

Immunological abnormalities in human immunodeficiency virus (HIV)-infected asymptomatic homosexual men. HIV affects the immune system before CD4+ T helper cell depletion occurs.

To investigate the effect of persistent HIV infection on the immune system, we studied leukocyte functions in 14 asymptomatic homosexual men (CDC group II/III) who were at least two years seropositive, but who still had normal numbers of circulating CD4+ T cells. Compared with age-matched heterosexual men and HIV-negative homosexual men, the CD4+ and CD8+ T cells from seropositive men showed decreased proliferation to anti-CD3 monoclonal antibody and decreased CD4+ T-helper activity on PWM-driven differentiation of normal donor B cells. Monocytes of HIV-infected homosexual men showed decreased accessory function on normal T cell proliferation induced by CD3 monoclonal antibody. The most striking defect in leukocyte functional activities was observed in the B cells of HIV-infected men. B cells of 13 out of 14 seropositive men failed to produce Ig in response to PWM in the presence of adequate allogeneic T-helper activity. These findings suggest that HIV induces severe immunological abnormalities in T cells, B cells, and antigen-presenting cells early in infection before CD4+ T cell numbers start to decline. Impaired immunological function in subclinically HIV-infected patients may have clinical implications for vaccination strategies, in particular the use of live vaccines in groups with a high prevalence of HIV seropositivity