Filarial infection modulates the immune response to mycobacterium tuberculosis through expansion of CD4+ IL-4 memory T cells

Exaggerated CD4⁺ T helper 2-specific cytokine producing memory T cell responses developing concomitantly with a T helper 1 response might have a detrimental role in immunity to infection caused by Mycobacterium tuberculosis. To assess the dynamics of Ag-specific memory T cell compartments in the context of filarial infection, we used multiparameter flow cytometry on PBMCs from 25 microfilaremic filarial-infected (Inf) and 14 filarial-uninfected (Uninf) subjects following stimulation with filarial Ag (BmA) or with the M. tuberculosis-specific Ag culture filtrate protein-10 (CFP-10). Our data demonstrated that the Inf group had a marked increase in BmA-specific CD4⁺IL-4⁺ cells (median net frequency compared with baseline [Fo] = 0.09% versus 0.01%; p = 0.038) but also to CFP-10 (Fo = 0.16% versus 0.007%; p = 0.04) and staphylococcal enterotoxin B (Fo = 0.49% versus 0.26%; p = 0.04). The Inf subjects showed a BmA-specific expansion of CD4⁺CD45RO+IL-4⁺ producing central memory (TCM, CD45RO+ CCR7⁺CD27⁺; Fo = 1.1% versus 0.5%; p = 0.04) as well as effector memory (TEM, CD45RO+CCR72CD272; Fo = 1.5% versus 0.2%; p = 0.03) with a similar but nonsignificant response to CFP-10. In addition, there was expansion of CD4⁺IL-4⁺CD45RA+ CCR7⁺CD27⁺ (naive-like) in Inf individuals compared with Uninf subjects. Among Inf subjects with definitive latent tuberculosis, there were no differences in frequencies of IL-4-producing cells within any of the memory compartments compared with the Uninf group. Our data suggest that filarial infection induces Ag-specific, exaggerated IL-4 responses in distinct T cell memory compartments to M. tuberculosis-specific Ags, which are attenuated in subjects who are able to mount a delayed type hypersensitivity reaction to M. tuberculosis.