The Tetraspanin Protein CD37 Regulates IgA Responses and Anti-Fungal Immunity
Figure 3
Increased IgA production after immunization in CD37−/− mice is dependent on IL-6.
(A) Immunohistochemical analysis of spleens from CD37−/− and WT mice 14 d after NP-KLH immunization. Germinal centers (identified in serial sections by PNA staining) are indicated in the B cell follicles. Immunized WT mice have non-detectable levels of IL-6 in spleens (left). In contrast, B cell follicles in spleens of immunized CD37−/− mice are clearly positive for IL-6 (red) in the GC area (right). Spleens of non-immunized mice (WT and CD37−/−) were negative for IL-6 staining (not shown). Scale bar is 50 µm. (B) Effect of neutralizing anti–IL-6 during ex vivo restimulation. Splenocytes from WT and CD37−/− mice were prepared 14 d after NP-KLH immunization, and stimulated in vitro with NP-KLH (1 µg/ml) in the absence or presence of anti–IL-6. Supernatants were collected after 48 h, and assayed for IgA production by ELISA (expressed in arbitrary units). Asterisk indicates significant difference (*p<0.002). (C) IL-6 was neutralized in WT and CD37−/− mice during immunizations using blocking IL-6 antibodies (as described in Materials and methods). High affinity NP-specific IgA was assayed in serum of CD37−/− mice treated with anti–IL-6 (black) or control antibody (white) (left). Antibody titer is expressed in arbitrary units and represented as mean±SEM (n = 6). Asterisks indicate significant difference as per: *p<0.04. Histogram shows percentage of CD37−/− mice with high IgA anti-NP3 levels (above 10× background level) in serum after treatment with anti–IL-6 (black) compared to control treated CD37−/− mice (white) at indicated days after immunization (right). Similar results were obtained for total NP-specific antibody (against NP20-BSA).