title: Depletion of immunoglobulin M memory B cells is associated with splenic hypofunction in inflammatory bowel disease.
abstract: OBJECTIVE
  IgM memory B cells that are responsible for the protection against infections by encapsulated bacteria, require the spleen for their generation and/or survival. Since the association between inflammatory bowel disease and functional hyposplenism is well described, our aim was to verify whether IgM memory B cells mirror the reduced splenic function in Crohn's disease and ulcerative colitis patients.
  
  
  METHODS
  Peripheral blood samples were obtained from 32 Crohn's disease and 29 ulcerative colitis patients, 33 healthy controls, and 27 splenectomized patients. Perendoscopic intestinal biopsies were also collected from 15 of 32 Crohn's disease patients, 14 of 29 ulcerative colitis patients and 13 of 33 control subjects. Counting of erythrocytes with membrane abnormalities (pitted red cells) was used as an indicator of splenic function and flow cytometry was performed to analyze both peripheral and mucosal B cells.
  
  
  RESULTS
  Twelve of 32 Crohn's disease patients and 13 of 29 ulcerative colitis patients had pitted red cell values >4% and were considered to be hyposplenic. In inflammatory bowel disease patients circulating IgM memory B cells were significantly lower than in control subjects. We observed a significant inverse correlation between the frequency of circulating IgM memory B cell and the pitted red cell values in inflammatory bowel disease patients with hyposplenism. To exclude the possibility that the reduction of circulating IgM memory B cells reflected their recruitment in the inflamed bowel mucosa, lamina propria B-cell populations were also characterized. We found that the frequency of IgM memory B cells was similar in the blood and in the lamina propria of the same patient.
  
  
  CONCLUSIONS
  Our findings show that peripheral IgM memory B cells are reduced in inflammatory bowel disease patients and this defect seems to be related to the impairment of splenic function.
authors.affiliation: Gastroenterology Unit, IRCCS Policlinico S. Matteo, University of Pavia, Pavia, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Di Sabatino
authors.forename: Maria Manuela
authors.initials: MM
authors.lastname: Rosado
authors.forename: Rachele
authors.initials: R
authors.lastname: Ciccocioppo
authors.forename: Paolo
authors.initials: P
authors.lastname: Cazzola
authors.forename: Raffaele
authors.initials: R
authors.lastname: Morera
authors.forename: Gino Roberto
authors.initials: GR
authors.lastname: Corazza
authors.forename: Rita
authors.initials: R
authors.lastname: Carsetti
mesh_terms: D000328:Adult; D000368:Aged; D001402:B-Lymphocytes / Q000276:immunology*; D005434:Flow Cytometry; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology*; D007156:Immunologic Memory; D015212:Inflammatory Bowel Diseases / Q000276:immunology* / Q000503:physiopathology; D008875:Middle Aged; D013154:Spleen / Q000503:physiopathology*; D013156:Splenectomy
chemical_list: D007075:Immunoglobulin M