Absence of specific alternatively spliced exon of CD44 in macrophages prevents colitis.

CD44 is a transmembrane molecule appearing in numerous isoforms generated by insertions of alternatively spliced variant exons (CD44v) and having various binding partners. CD44v7 on T cells was proposed to promote colitis by preventing T-cell apoptosis. Here we demonstrate that Cd44v7-deficient T cells - like Cd44 wild-type (Cd44WT) T cells - provoked disease in two different colitis models: the model induced by CD4+CD45RBhigh T-cell transfer into Rag2-deficient mice and a new model based on ovalbumin (OVA)-specific T-cell transfer into Rag-sufficient, OVA-challenged mice. In contrast, CD44v7 absence on macrophages in recipient mice prevented colitis. Prevention was associated with the downregulation of signal transducer and activator of transcription 3 (STAT3)-activating and Foxp3-counteracting interleukin-6 (IL-6), lower numbers of phospho-STAT3-containing lymphocytes, and higher Foxp3+ T-cell counts in the colon. Consequently, the protected colons showed lower IL-12, IL-1ß expression, and decreased interferon-γ levels. Importantly, stimulation of T cells by Cd44v7-deficient macrophages induced upregulation of Foxp3 in vitro, while cotransfer of Cd44WT macrophages into Cd44v7-deficient mice reduced Foxp3+ T-cell counts and caused colitis. Accordingly, the CD44v7 ligand osteopontin, whose levels were elevated in Crohn's disease, specifically induced IL-6 in human monocytes, a cytokine also increased in these patients. We suggest macrophage-specific targeting of the CD44v7 pathway as a novel therapeutic option for Crohn's disease.

IgA antibody production by intrarectal immunization of mice using recombinant major capsid protein of hamster polyomavirus.

Viral proteins are highly antigenic and known as potent stimulators of adaptive immune responses. This mechanism is often used for biotechnological applications in monoclonal antibody production resulting in high-affinity IgG antibodies in most cases. The aim of this study was to increase antigen-specific IgA antibody levels in mice in order to generate monoclonal IgA antibodies by hybridoma technology. For this purpose, hamster polyomavirus (HaPyV) major capsid protein VP1 was used to immunize mice by different routes in order to induce VP1-specific IgA titers. Recombinant HaPyV-VP1 was generated in Escherichia coli and administered intraperitoneally, orally, and intrarectally. VP1-specific antibodies were determined by ELISA in sera and organ culture supernatants. We found a significant increase of HaPyV-VP1-specific IgAs in spleen organ cultures after rectal immunization of mice but not in cultures of mesenteric lymph nodes, colon, or Peyer's patches. In contrast, oral and intraperitoneal immunization did not provide an appropriate specific IgA induction at all. These results show that specific IgA antibodies can be induced by intrarectal immunization in the spleen. The generation of monoclonal IgA antibodies with well-defined properties is a useful tool for the investigation of mucosal immune responses or autoimmune diseases and extends the spectrum of antibodies with specific effector functions.