Extrafollicular Plasmablasts Present in the Acute Phase of Infections Express High Levels of PD-L1 and Are Able to Limit T Cell Response.

During infections with protozoan parasites or some viruses, T cell immunosuppression is generated simultaneously with a high B cell activation. It has been described that, as well as producing antibodies, plasmablasts, the differentiation product of activated B cells, can condition the development of protective immunity in infections. Here, we show that, in T. cruzi infection, all the plasmablasts detected during the acute phase of the infection had higher surface expression of PD-L1 than other mononuclear cells. PD-L1hi plasmablasts were induced in vivo in a BCR-specific manner and required help from Bcl-6+CD4+T cells. PD-L1hi expression was not a characteristic of all antibody-secreting cells since plasma cells found during the chronic phase of infection expressed PD-L1 but at lower levels. PD-L1hi plasmablasts were also present in mice infected with Plasmodium or with lymphocytic choriomeningitis virus, but not in mice with autoimmune disorders or immunized with T cell-dependent antigens. In vitro experiments showed that PD-L1hi plasmablasts suppressed the T cell response, partially via PD-L1. Thus, this study reveals that extrafollicular PD-L1hi plasmablasts, whose peaks of response precede the peak of germinal center response, may have a modulatory function in infections, thus influencing T cell response.

Inhibitory Receptor Expression on T Cells as a Marker of Disease Activity and Target to Regulate Effector Cellular Responses in Rheumatoid Arthritis.

OBJECTIVE: Inhibitory receptors are essential for the regulation of effector immune responses and may play critical roles in autoimmune diseases. We evaluated whether inhibitory receptor expression on T cells from patients with rheumatoid arthritis (RA) were correlated with immune activation, disease activity, and response to treatment, as well as whether inhibitory receptor-mediated pathways were functional. METHODS: Using flow cytometry, we performed extensive phenotypic and functional evaluation of CD4+ and CD8+ T cells from the blood and synovial fluid (SF) of RA patients ex vivo and after culture. The relationship of each parameter with the Disease Activity Score in 28 joints using the erythrocyte sedimentation rate (DAS28-ESR) and response to treatment was examined. RESULTS: In RA patients with low levels of T cell activation, inhibitory receptor expression showed an inverse relationship with the DAS28-ESR. The frequency of T cells expressing multiple inhibitory receptors was reduced in untreated RA patients but returned to normal levels in treated patients. RA patients who responded to treatment showed an augmented frequency of inhibitory receptor-expressing T cells that correlated with reduced inflammatory cytokine production in comparison to nonresponders. Higher frequencies of effector and memory T cells that expressed multiple inhibitory receptors were seen in SF than in peripheral blood. Notably, inhibitory pathways were operative in blood and synovial T cells from all RA patients, although cells from nonresponder patients were less sensitive to inhibition. CONCLUSION: Inhibitory receptor expression on T cells from RA patients is inversely correlated with effector T cell function and disease activity and may predict response to treatment. Furthermore, different inhibitory pathways are functional and cooperatively suppress synovial T cells, providing a rationale for new treatment strategies to regulate acute local inflammation.