title: The loss of IgM memory B cells correlates with clinical disease in common variable immunodeficiency.
abstract: BACKGROUND
  Recurrent lower respiratory tract infections caused by encapsulated bacteria might cause permanent organ damage in patients with common variable immunodeficiency (CVID). Despite the profound hypogammaglobulinemia, some patients do not experience bacterial pneumonia. We have shown that IgM memory B cells and natural antibodies play an important role in the defense against encapsulated bacteria.
  
  
  OBJECTIVE
  In this study we addressed the question of whether the apparent paradox of patients with severe hypogammaglobulinemia but no increased frequency of respiratory infections can be explained by the presence of IgM memory B cells and anti-pneumococcal polysaccharide (anti-PnPS) IgM.
  
  
  METHODS
  We measured the frequency of memory B cells and the levels of anti-PnPS IgM antibodies in 26 patients with CVID with recurrent bacterial pneumonia and bronchiectasis (group 1) and 22 who never had pneumonia and showed no lung lesions (group 2). An additional 6 patients had a clinical history of recurrent pneumonia without lung abnormalities at computed tomographic scanning.
  
  
  RESULTS
  Patients of group 1 lacked IgM memory B cells and failed to produce anti-PnPS IgM antibodies, and those of group 2 had a normal frequency of IgM memory B cells and produced anti-PnPS IgM antibodies.
  
  
  CONCLUSIONS
  IgM memory B cells and anti-PnPS IgM antibodies protect patients with CVID from bacterial pneumonia. Evaluation of these 2 parameters discriminates patients with low or high risk of recurrent infections caused by encapsulated bacteria and low or high risk of bronchiectasis. Identification of high-risk individuals at diagnosis might help in the planning of a more effective therapeutic strategy and prevent permanent organ damage.
authors.affiliation: Research Center, Ospedale Pediatrico Bambino Gesù, Rome, Italy. Rita.Carsetti@uniroma2.it
authors.forename: Rita
authors.initials: R
authors.lastname: Carsetti
authors.forename: Maria Manuela
authors.initials: MM
authors.lastname: Rosado
authors.forename: Simona
authors.initials: S
authors.lastname: Donnanno
authors.forename: Vanessa
authors.initials: V
authors.lastname: Guazzi
authors.forename: Annarosa
authors.initials: A
authors.lastname: Soresina
authors.forename: Antonella
authors.initials: A
authors.lastname: Meini
authors.forename: Alessandro
authors.initials: A
authors.lastname: Plebani
authors.forename: Fernando
authors.initials: F
authors.lastname: Aiuti
authors.forename: Isabella
authors.initials: I
authors.lastname: Quinti
mesh_terms: D000293:Adolescent; D000328:Adult; D016175:B-Lymphocyte Subsets / Q000276:immunology / Q000473:pathology; D001402:B-Lymphocytes / Q000276:immunology* / Q000473:pathology*; D001428:Bacterial Vaccines / Q000627:therapeutic use; D002648:Child; D015331:Cohort Studies; D017074:Common Variable Immunodeficiency / Q000188:drug therapy / Q000276:immunology* / Q000473:pathology*; D005260:Female; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology*; D007156:Immunologic Memory; D008297:Male; D008875:Middle Aged; D011135:Polysaccharides, Bacterial / Q000276:immunology / Q000378:metabolism; D013296:Streptococcus pneumoniae / Q000276:immunology / Q000378:metabolism; D014611:Vaccination
chemical_list: D001428:Bacterial Vaccines; D007075:Immunoglobulin M; D011135:Polysaccharides, Bacterial