Assessment of the IgA and IgG response against commensal microbiota during the development of the dextran sulfate sodium-induced colitis.

LISA MACCIO MARETTO, IVANNA NOVOTNY NUÑEZ, BIBIANA E BARRIOS, AND SILVIA G CORREA

Mar del Plata

Congreso; Reunión Anual Conjunta SAIC-SAI-SAFE; 2016

SAIC-SAI-SAFE

Intestinal macrophages (MΦs) are the most abundant population of resident phagocytic cells in the gut. They can be identified by the expression of either CD11b, F4/80 or CD64 markers and play an important role in the intestinal immunity. Recently, it has been shown that IgG against commensal microbiota may contribute to the intestinal homeostasis. Herein, we evaluated the canonical IgA response as well as the production of IgG to luminal microorganisms in untreated WT mice (control group) or after 5 days of administrating dextran sulfate sodium (colitis group). During the 7 day-period of colitis development we collected feces from both groups and we analyzed IgG+ and IgA+ bacteria by flow cytometry. On day 7 of the colitis we isolated mononuclear cells from lamina propria by mild collagenase digestion and we evaluated a) the frequency of CD138+IgG+ plasmatic cells and b) the uptake of immune complexes (IgG-Ag) in CD11b+ F4/80+ permeabilized MΦs. Compared with control group the percentage of IgA-coated bacteria did not vary on colitis mice while the percentage of IgG-coated microorganisms was significantly lower with the ongoing inflammation (p<0.01). Interestingly, the frequency of bacteria coated with both antibodies increased significantly already on day 2 and this increment persisted on days 4 and 5 (p<0.05), when the barrier permeability is critically affected. The frequency of CD138+IgG+ plasmatic cells in lamina propria of WT and colitis groups was similar while a reduction in the frequency of CD11b+ MΦs with intracellular IgG was observed (p=0.027); the intracellular IgG in CD11b+ MΦs evaluated as MFI was also reduced by the intestinal inflammation (p=0.012).These results show that CD138+ IgG+ are constitutively located in lamina propia and that their frequency is not modified in colitis. Fast changes in the proportion of IgG in the lumen and immune complexes in phagocytic CD11b+ cells become sensitive markers of the ongoing acute inflammatory disease.