Inflammasome and Th17 activation in HIV+ immunological nonresponders

Background: Inflammasomes are multimeric protein platforms involved in the regulation of inflammatory responses. Inflammasome activity results in the production of proinflammatory cytokines and in Th17 activity (Mills K.H.G. et al, JLB 2013; Peelen E. et al, Molecular Immunology 2015); its role in immune reconstitution in HIV+ patients is nevertheless unclear. We analyzed possible associations between inflammasomes or Th17 activation and the degree of immune reconstitution in HIV+ patients. Methods: Cross-sectional, single-site study enrolling HIV-infected patients on antiretroviral therapy for ≥24 months and plasma HIV-RNA<50cp/mL for ≥12 months. Exclusion criteria: presence of actual opportunistic AIDS-related diseases, HBV or HCV coinfection, chronic inflammatory disorders, ongoing immunosuppressive therapy. Patients were classified as immunological responders (IR) or non responders (INR) if CD4 count was ≥500 or ≤350 cells/µL, respectively. Immune activation markers (HLA-DRII, CD38 and Ki-67), Th17 activity and expression of genes involved in the inflammasome pathway were measured in unstimulated or LPS- and AT2-stimulated cells. Results: Thirty-nine patients (22 IR and 17 INR, 76.9% males, medians:  age 47 years, time from HIV diagnosis 10 years, time with HIV-RNA<50cp/mL 57 months) were enrolled. INR patients were older (median 60 vs. 43 years, p<0.001) and had a higher prevalence of past AIDS-defining illnesses (76.5% vs. 18.2%, p<0.001) compared to IR patients. Median CD4 count was 840 (IQR 718-1131) cells/µL in IR vs. 295 (IQR 256-343) cells/µL in INR. LPS-stimulated inflammasomes (NLRP3 and NLRP1) and pro-inflammatory cytokines expression (IL-1β, IL-18, TNFα, type-I IFNs, CCL3, IL-6) were significantly increased in INR patients. Higher median levels of Th17 lymphocytes (CD4/IL17A/RORgT) were also seen in INR in unstimulated (0.32% vs. 0.19%, p=0.045), as well as in LPS- (0.60% vs 0.22%, p=0.011), and AT2- (0.67% vs 0.17%, p=0.006) stimulated conditions. Finally, HLADRII/CD4 (12.48% vs. 5.86%, p=0.025) were significantly increased in unstimulated cell cultures of INR. Immune recovery was independently associated with lower Th17 levels (mean change -0.42%, p=0.005) after adjustment for age and past AIDS. Conclusions: Higher levels of inflammasome factors, an increased percentage of Th17 and immune activation characterize the immune scenario of ART-treated INR patients. These alterations are likely to contribute to the lack of CD4 recovery seen in INR.