Intricate properties of memory B cell development after oral immunization (MUC4P.836)

Abstract

Abstract Recent debate over the ability to generate memory B cells in the gut immune system prompted us to explore a novel model with transgenic NP-hapten-specific GFP+ B cells and oral immunizations with NP-conjugated to cholera toxin (NP-CT). We found that orally immunized mice developed exceptional long term memory B cell populations that resided in B cell follicles in Peyer’s patches, mesenteric lymph nodes and spleen. A majority of the GFP+ memory cells, defined by CD80, CD73 and PD-L2 expression, were IgM+, but also a significant number were IgA+ and in spleen IgG+ memory B cells were frequent. Upon analysis of the NP binding VH186.2 IgA gene sequences between 20-40 % carried high affinity mutations and VH186.2 IgG (bone marrow) and IgA (intestine and bone marrow) gene sequences were clonally related. A challenge immunization after 1.5 years, either orally or i.p, elicited a strong NP-specific gut lamina propria (LP) IgA and serum IgG response, starting from a calculated frequency of 1 NP-memory / total 10.000 B cells in these mice. Gut LP IgA plasma cells increased after challenge from 0.05% long-lived NP-specific IgA plasma cells to >5% NP-specific IgA plasma cells of all LP IgA plasma cells. The boosted IgA plasma cells carried more mutations and higher affinities (>60%) than long-lived memory B cells, demonstrating unexpectedly effective selection and maturational processes in gut IgA memory responses.