Genetic Control of the Humoral Responses to Xenografts. Iii. Identification of the Immunoglobulin Vh Genes Responsible for Encoding Rat Immunoglobin G Xenoantibodies to Hamster Heart Grafts1

Abstract

The change in IgM to IgG antibody production in the later stages of the humoral immune response of rats to hamster xenografts is associated with an IgM to IgG isotype switch and an increased production of antibodies of the IgG1 isotype. Rat anti-hamster IgG xenoantibodies continue to express the V(H)HAR family of V(H) genes, many in their original germline configuration, to encode antibody recognition of the hamster target antigens. There are, however, a majority of antibodies for which the V(H) genes express evidence of increased nucleic acid sequence variation when compared to currently available germline sequences. The source of this variation is not known but may represent the expression of as yet unidentified germline genes and/or the introduction of T cell-driven somatic mutations. Despite the appearance of this variation, the unusual level of conservation in key antigen binding sites within the V(H) region suggests the variation, independent of its origin, may have a limited influence on the restricted nature of the host antibody response to xenografts.

Maturation of xenoantibody gene expression during the humoral immune response of rats to hamster xenografts

“…We demonstrated that a major production of rat anti‐hamster xenoantibodies is encoded by a closely related group of Ig V H genes (V H HAR family). The majority of these rearranged V H µ genes were expressed in their original germline configuration [19]. The finding is in general agreement with the hypothesis that primary IgM response to xenografts reflects the expression of a primitive, T cell independent antibody production originally developed to provide a rapid but relatively nonspecific response to infection.…”

“…V H HAR + µ chain cDNA libraries were made from spleen B cells of LEW recipients of hamster heart grafts at day 4, whereas V H HAR + γ chain cDNA libraries were from animals at day 21 PTx. The methods for construction of Ig V H cDNA libraries have been described in our earlier publications [18,19]. Briefly, total mRNA was isolated from approximately 5 × 10 6 splenocytes using a modified guan‐idium isothiocyanate method.…”

“…A germline V H gene with the highest nucleotide sequence identity for a specific rearranged V H gene was considered to be the germline precursor of that particular rearranged V H gene. A rearranged V H gene, showing an identity of 98% or higher to a germline gene, is considered as being encoded by that particular germline gene in non‐mutated form or germline configuration [19,27].…”

“…On the other hand, data provided by others had suggested that subsequent IgG responses in the hamster/rat model were T‐dependent [20,21]. We have recently found that V H γ genes encoding xenoreactive IgG antibodies during secondary response to hamster heart graft display increased nucleotide variation when compared with their progenitor germline genes [19]. The extent and the nature of such nucleotide variation have not been carefully analyzed.…”

Antibody Mediated Rejection in Pig-To-Nonhuman Primate Xenotransplantation Models

“…Following transplantation, after reaching peak levels in the second week, the IgM titers decline and the IgG switch may occur. In this regard, it is noteworthy that the detected IgG antibodies express V H genes of the same family, many in their original germline configuration, although the majority of the elicited IgG antibodies present somatic mutations [105]. This data indicates that both Tdependent and T-independent immune responses are eventually involved in determining the elicited antibody repertoire.…”