title: IgA class switch occurs in the organized nasopharynx- and gut-associated lymphoid tissue, but not in the diffuse lamina propria of airways and gut.
abstract: Secretory IgA plays a crucial role in the host immune response as a first line of defense. A recent demonstration of in situ IgA class switching in intestinal lamina propria provided an opportunity to reconsider the model for the homing of IgA-committed B cells characterized by distinctive trafficking patterns to effector sites. Those effector sites depend on the organized mucosa-associated lymphoid tissues as their site of induction. In this report we show the preferential presence of IgM(+)B220(+) and IgA(+)B220(+) cells belonging to pre- and post-IgA isotype class-switched cells in the organized mucosa-associated lymphoid tissues, such as nasopharynx-associated lymphoid tissues, isolated lymphoid follicles, and Peyer's patches, and the defect of those populations in the diffuse effector tissues, such as the nasal passage and intestinal lamina propria. Consistent with these findings, the expressions of a series of IgA isotype class switch recombination-related molecules, including activation-induced cytidine deaminase, Ialpha-C micro circle transcripts, and Ialpha-C micro circle transcripts, were selectively detected in these organized mucosa-associated lymphoid structures, but not in the diffuse mucosal effector sites. Taken together, these findings suggest that IgA isotype class switching occurs only in the organized mucosa-associated lymphoid organs (e.g., nasopharynx-associated lymphoid tissues, isolated lymphoid follicles, and Peyer's patches), but not in the diffuse effector tissues of the upper respiratory and gastrointestinal tracts.
authors.affiliation: Department of Mucosal Immunology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Shikina
authors.forename: Takachika
authors.initials: T
authors.lastname: Hiroi
authors.forename: Kohichi
authors.initials: K
authors.lastname: Iwatani
authors.forename: Myoung Ho
authors.initials: MH
authors.lastname: Jang
authors.forename: Satoshi
authors.initials: S
authors.lastname: Fukuyama
authors.forename: Manabu
authors.initials: M
authors.lastname: Tamura
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kubo
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kiyono
mesh_terms: D000818:Animals; D016175:B-Lymphocyte Subsets / Q000276:immunology / Q000378:metabolism; D018928:Immunity, Mucosal / Q000235:genetics; D007070:Immunoglobulin A / Q000096:biosynthesis*; D017578:Immunoglobulin Class Switching / Q000235:genetics; D007075:Immunoglobulin M / Q000096:biosynthesis; D007413:Intestinal Mucosa / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D007421:Intestine, Small / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D017493:Leukocyte Common Antigens / Q000096:biosynthesis; D008221:Lymphoid Tissue / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009297:Nasal Mucosa / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D009305:Nasopharynx / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D010581:Peyer's Patches / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D011995:Recombination, Genetic / Q000276:immunology; D020545:Respiratory Mucosa / Q000166:cytology / Q000276:immunology* / Q000378:metabolism
chemical_list: D007070:Immunoglobulin A; D007075:Immunoglobulin M; D012333:RNA, Messenger; D017493:Leukocyte Common Antigens