Background Infliximab and etarnecept are now widely used for treating severe psoriasis. However, these drugs, especially infliximab, increased the risk of tuberculosis reactivation. Surprisingly, epidemiological data suggest that the tuberculosis rate in patients taking infliximab in São Paulo State, Brazil, is similar to that of some developed, non-endemic countries.
Objective The aim of this study was to better understand the effect of infliximab on Mycobacterium tuberculosis (Mtb) immune responses of psoriasis patients in an endemic setting (Brazil).
Methods We evaluated the tuberculosis-specific immune responses of severe psoriasis patients and healthy individuals, both tuberculin skin test (TST) positive, in the presence/absence of infliximab. Patients had untreated severe psoriasis, no co-morbidities affecting the immune responses and a TST >10 mm. Healthy TST+ (>10 mm) individuals were evaluated in parallel. PBMC cultures from both groups were stimulated with different Mycobacterium tuberculosis (Mtb) antigens (ESAT-6, 85B and Mtb lysate) and phytohemagglutinin, with or without infliximab (5 μg/mL). Parameters evaluated were TNF-α, IFN-γ and IL-10 secretion by ELISA, overnight IFN-γ ELISpot and lymphocyte proliferative response (LPR).
Results Infliximab almost abolished TNF-α detection in PBMC supernatants of both groups. It also significantly reduced the LPR to phytohemagglutinin and the Mtb antigens as well as the IFN-γ levels secreted into day 5 supernatants in both groups. There was no concomitant exaggerated IL-10 secretion that could account for the decreases in these responses. ELISpot showed that, contrasting with the central-memory responses above, infliximab did not affect effector-memory INF-γ-releasing T-cell numbers.
Conclusions Infliximab affected some, but not all aspects of the in vitro antituberculosis immune responses tested. The preserved effector-memory responses, putatively related to exposure to environmental mycobacteria, may help to explain the lower than expected susceptibility to tuberculosis reactivation in our setting.