Antibody Repertoire Development in Fetal and Neonatal Piglets: XIX. Undiversified B Cells with Hydrophobic HCDR3s Preferentially Proliferate in the Porcine Reproductive and Respiratory Syndrome

Abstract

Porcine respiratory and reproductive syndrome virus (PRRSV) causes an extraordinary increase in the proportion of B cells resulting in lymphoid hyperplasia, hypergammaglobulinemia, and autoimmunity in neonatal piglets. Spectratypic analysis of B cells from neonatal isolator piglets show a non-Gaussian pattern with preferential expansion of clones bearing certain H chain third complementary region (HCDR3) lengths. However, only in PRRSV-infected isolator piglets was nearly the identical spectratype observed for all lymphoid tissues. This result suggests dissemination of the same dominant B cell clones throughout the body. B cell expansion in PRRS was not associated with preferential VH gene usage or repertoire diversification and these cells appeared to bear a naive phenotype. The B cell population observed during infection comprised those with hydrophobic HCDR3s, especially sequences encoded by reading frame 3 of DHA that generates the AMVLV motif. Thus, the hydropathicity profile of B cells after infection was skewed to favor those with hydrophobic binding sites, whereas the normally dominant region of the hydropathicity profile containing neutral HCDR3s was absent. We believe that the hypergammaglobulinemia results from the products of these cells. We speculate that PRRSV infection generates a product that engages the BCR of naive B cells, displaying the AMVLV and similar motifs in HCDR3 and resulting in their T-independent proliferation without repertoire diversification.

Porcine Reproductive and Respiratory Syndrome Virus Subverts Repertoire Development by Proliferation of Germline-Encoded B Cells of All Isotypes Bearing Hydrophobic Heavy Chain CDR3

“…More recently, we have shown that this syndrome is also associated with the apparent dissemination of certain B cell clones throughout the body (see Fig. 2) that preferentially bear BCRs with hydrophobic H chain CDR3 (HCDR3) regions (6). Skewing of hydropathicity profiles toward B cells with hydrophobic binding sites is unusual in mice and humans (7)(8)(9) and was not observed in littermates infected with SIV, sham controls, young pigs infected with helminthic parasites, or in newborn piglets (6).…”

“…2) that preferentially bear BCRs with hydrophobic H chain CDR3 (HCDR3) regions (6). Skewing of hydropathicity profiles toward B cells with hydrophobic binding sites is unusual in mice and humans (7)(8)(9) and was not observed in littermates infected with SIV, sham controls, young pigs infected with helminthic parasites, or in newborn piglets (6). However, that study did not randomly sample B cell clones, so the size of the subpopulation could not estimated and the source of the expanded clones with regard to either V H gene usage or isotype expression was not identified.…”

“…Because of this limited combinatorial diversity, the BCR repertoire is overwhelmingly determined by HCDR3 diversity (21). Diversity in HCDR3 lengths is a quasi-clone marker, so spectratypic analysis (HCDR3 length analysis) provides a quasiclonotypic analysis (6,22). The HCDR3 segments from VDJs expressed with IgA, IgM, and IgG from the same tissue sample from the same animal were recovered by PCR and the products were spectratyped side-by-side so that the profiles for IgA, IgM, and IgG could be compared.…”

B Cell Lymphogenesis in Swine Is Located in the Bone Marrow

“…Separation of CDR3 regions for Ig HCs on polyacrylamide sequencing gels provides a clonotypic analysis of BCR repertoire (22,23). This procedure is called CDR3 length analysis or spectratyping and was performed on unsorted or sorted B-lineage populations to show their level of selection for IF rearrangements (18).…”

“…This procedure is called CDR3 length analysis or spectratyping and was performed on unsorted or sorted B-lineage populations to show their level of selection for IF rearrangements (18). Technically, the CDR3 segments of the amplified VDJs from DNA were reamplified in the third round of PCR using an FR3 up primer that anneals to all porcine V H genes and a [ 32 P]-labeled J H down primer (22,23). The products were separated on sequencing gels that were dried and images were obtained by fluorescent image analyzer FLA-7000 (Fujifilm, Tokyo, Japan).…”