The largest mucosal surface in the body is in the gastrointestinal (GI) tract, a location that is heavily colonized by normally harmless microbes. A key mechanism required for maintaining a homeostatic balance between this microbial burden and the lymphocytes that densely populate the GI tract is the production and trans-epithelial transport of poly-reactive IgA1. Within the mucosal tissues, B cells respond to cytokines, sometimes in the absence of T cell help, undergo class switch recombination (CSR) of their Immunoglobulin (Ig) receptors to IgA, and differentiate to become plasma cells (PC)2. However, IgA-secreting PC likely have additional attributes that are needed for coping with the tremendous bacterial load in the GI tract. We report that IgA+ PC also can produce the anti-microbial mediators TNFα and iNOS, which appear to arise in the unique environment of the gut, and may be critical to mount effective responses to microbial assault.
Here we described a detailed method to characterize and quantify IgA+iNOS+TNFα+ cells that we called TNFα-iNOS-producing (Tip)-PC in the lamina propria of mice by immunohistochemistry (IHC).