Analysis of cytokine production by Mycobacterium-reactive T cells: Failure to explain Mycobacterium leprae-specific nonresponsiveness of peripheral blood T cells from lepromatous leprosy patients

Recent analyses of antimycobacterial T cell clones from a small number of individuals indicate that mycobacteria preferentially induce Th cells that produce high levels of IFN-γ and no or little IL-4 in Mycobacterium leprae- resistant tuberculoid leprosy (TT) patients and healthy subjects, whereas in one study M. leprae-induced Ts clones from polar lepromatous leprosy (LL) patients showed a reciprocal cytokine secretion profile and mediated their suppressive activity via the release of high levels of IL-4. We have evaluated these findings in peripheral blood T cells from a larger panel of TT and LL patients as well as healthy individuals. Mycobacterium-reactive T cell lines generated from the PBMC of these individuals were tested for cytokine secretion and proliferative capacity in response to M. leprae, Mycobacterium tuberculosis, and various individual mycobacterial Ag. The lepromatous pole of the leprosy spectrum was additionally investigated by analyzing the cytokine-secretion profile of M. leprae-induced (suppressor) T cell clones as well as primary ex vivo PBMC. All T cell lines from healthy individuals and TT patients responding to M. leprae, M. tuberculosis, or individual Ag, produced high levels of IFN-γ and TNF-α but little or no IL- 4 and IL-6. At the lepromatous pole, T cell lines failed to proliferate upon stimulation with M. leprae but in some cases produced significant levels of IFN-γ. No IL-4 or IL-6 secretion was observed in response to M. leprae. These lines displayed strong proliferation and Th1-like cytokine production upon stimulation with M. tuberculosis. Similarly, stimulation of primary PBMC from LL patients with M. leprae or M. tuberculosis resulted in the release of IFN-γ but no detectable IL-4 production. Control tetanus toxoid-reactive T cell lines from the same individuals instead produced large amounts of IL-4 and low levels of IFN-γ. The analysis of M. leprae-induced T cell clones, including those with known suppressive activity, revealed that all lepromatous T cell clones produced large amounts of IFN-γ. Most of these clones released no or little IL-4, but some clones produced higher levels of IL-4 in addition to IFN-γ. Most clones tested produced IL-10 as well. The suppressor activity of suppressor T cell clones could not be inhibited by a neutralizing anti-IL-4 antibody and only in one case by neutralizing anti- IL-10 antibody. Anti-IL-4 and anti-IL-10 could not overcome the M. leprae- specific unresponsiveness observed in primary PBMC from LL patients. These results show that mycobacteria preferentially induce Th1-like cells across the whole leprosy spectrum. Although some T cells from lepromatous leprosy patients secrete IFN-γ as well as IL-4 and/or IL-10, neither IL-4 or IL-10 seems to play a pivotal role in the M. leprae-specific T cell unresponsiveness observed in the peripheral blood of lepromatous leprosy patients.