title: An antibody-deficiency syndrome due to mutations in the CD19 gene.
abstract: BACKGROUND
  The CD19 protein forms a complex with CD21, CD81, and CD225 in the membrane of mature B cells. Together with the B-cell antigen receptor, this complex signals the B cell to decrease its threshold for activation by the antigen.
  
  
  METHODS
  We evaluated four patients from two unrelated families who had increased susceptibility to infection, hypogammaglobulinemia, and normal numbers of mature B cells in blood. We found a mutation in the CD19 gene in all four patients. The CD19 gene in the patients and their first-degree relatives was sequenced, and flow-cytometric immunophenotyping of B cells, immunohistochemical staining of lymphoid tissues, and DNA and messenger RNA analysis were performed. B-cell responses on the triggering of the B-cell receptor were investigated by in vitro stimulation; the antibody response after vaccination with rabies vaccine was also studied.
  
  
  RESULTS
  All four patients had homozygous mutations in the CD19 gene. Levels of CD19 were undetectable in one patient and substantially decreased in the other three. Levels of CD21 were decreased, whereas levels of CD81 and CD225 were normal, in all four patients. The composition of the precursor B-cell compartment in bone marrow and the total numbers of B cells in blood were normal. However, the numbers of CD27+ memory B cells and CD5+ B cells were decreased. Secondary follicles in lymphoid tissues were small to normal in size and had a normal cellular composition. The few B cells that showed molecular signs of switching from one immunoglobulin class to another contained V(H)-C(alpha) and V(H)-C(gamma) transcripts with somatic mutations. The response of the patients' B cells to in vitro stimulation through the B-cell receptor was impaired, and in all four patients, the antibody response to rabies vaccination was poor.
  
  
  CONCLUSIONS
  Mutation of the CD19 gene causes a type of hypogammaglobulinemia in which the response of mature B cells to antigenic stimulation is defective.
authors: Department of Immunology, Erasmus MC, The Netherlands.
authors: Menno C
authors: MC
authors: van Zelm
authors: Ismail
authors: I
authors: Reisli
authors: Mirjam
authors: M
authors: van der Burg
authors: Diana
authors: D
authors: Castaño
authors: Carel J M
authors: CJ
authors: van Noesel
authors: Maarten J D
authors: MJ
authors: van Tol
authors: Cristina
authors: C
authors: Woellner
authors: Bodo
authors: B
authors: Grimbacher
authors: Pablo J
authors: PJ
authors: Patiño
authors: Jacques J M
authors: JJ
authors: van Dongen
authors: José L
authors: JL
authors: Franco