Molecular analysis of the heavy chain of antibodies that recognize the capsular polysaccharide of Neisseria meningitidis in hu-PBMC reconstituted SCID mice and in the immunized human donor

The severe combined immunodeficient (SCID) mouse model, engrafted with huma n peripheral blood mononuclear cells (hu-PBMC) has proven to be useful in s tudying the human immune response. A major limitation of the hu-PBMC-SCID m odel has been the failure to consistently demonstrate a primary human immun e response. Previously we developed a hu-PBMC-SCID mouse model in which we addressed both issues of adequate human lymphocyte engraftment and impaired differentiation. We demonstrated that a primary human immune response to t he T-independent (TI-2) meningococcal group C capsular polysaccharide (MCPS ) can be obtained in hu-PBMC-SCID mice by the administration of human cytok ines. Tn this study we compared the V-11 sequence of the MCPS response gene rated by B cells derived from a volunteer in the SCID mouse model to those generated by the donors' B cells in vivo. Human peripheral blood mononuclea r cells were recovered from MCPS immunized hu-PBMC-SCID mice and immunized donor. B cells with specificity for MCPS were isolated from these cell prep arations using an anti-idiotypic monoclonal antibody which mimics MCPS, Imm unoglobulin mRNA was isolated from single cells, amplified by the polymeras e chain reaction, cloned and sequenced. We analysed a total of 15 V-H regio ns from B cells obtained from SCID mice and a total of 13 V-H regions from B cells obtained from the immunized donor. The response differed between SC ID and in vivo cells, when studied at the genetric level. V, D and J gene u sage was markedly different, however canonical structures of the hypervaria ble loops were conserved. The complementary determining region 3 (CDR3) var ied, such that SCID-derived sequences encoded longer CDR3 s than those of t he donor. However all CDR3 s were rich in hydrophobic amino acids, most not ably tyrosine and tryptophan, a characteristic common to many carbohydrate binding antibodies. (C) 1999 Elsevier Science Ltd. All rights reserved.