<i>Nfkb2</i> deficiency and its impact on plasma cells and immunoglobulin expression in murine small intestinal mucosa.

The alternative (noncanonical) nuclear factor-κB (NF-κB) signaling pathway predominantly regulates the function of the p52/RelB heterodimer. Germline <i>Nfkb</i>2 deficiency in mice leads to loss of p100/p52 protein and offers protection against a variety of gastrointestinal conditions, including azoxymethane/dextran sulfate sodium (DSS)-induced colitis-associated cancer and lipopolysaccharide (LPS)-induced small intestinal epithelial apoptosis. However, the common underlying protective mechanisms have not yet been fully elucidated. We applied high-throughput RNA-Seq and proteomic analyses to characterize the transcriptional and protein signatures of the small intestinal mucosa of naïve adult <i>Nfkb2</i>^-/- mice. Those data were validated by immunohistochemistry and quantitative ELISA using both small intestinal tissue lysates and serum. We identified a B-lymphocyte defect as a major transcriptional signature in the small intestinal mucosa and immunoglobulin A as the most downregulated protein by proteomic analysis in <i>Nfkb2</i>^-/- mice. Small intestinal immunoglobulins were dramatically dysregulated, with undetectable levels of immunoglobulin A and greatly increased amounts of immunoglobulin M being detected. The numbers of IgA-producing, cluster of differentiation (CD)138-positive plasma cells were also reduced in the lamina propria of the small intestinal villi of <i>Nfkb2</i>^-/- mice. This phenotype was even more striking in the small intestinal mucosa of <i>RelB</i>^-/- mice, although these mice were equally sensitive to LPS-induced intestinal apoptosis as their <i>RelB</i>^+/+ wild-type counterparts. NF-κB2/p52 deficiency confers resistance to LPS-induced small intestinal apoptosis and also appears to regulate the plasma cell population and immunoglobulin levels within the gut.<b>NEW &amp; NOTEWORTHY</b> Novel transcriptomic analysis of murine proximal intestinal mucosa revealed an unexpected B cell signature in <i>Nfkb2</i>^-/- mice. In-depth analysis revealed a defect in the CD38+ B cell population and a gut-specific dysregulation of immunoglobulin levels.