Blood and colostral IgM and IgG B cell repertoires in high, average, and low immune responder Holstein Friesian cows and heifers.

In dairy cattle, genetic selection for higher antibody-mediated (AMIR) and cell-mediated (CMIR) immune responses can enhance disease resistance. Cattle produce a unique subset of B cells with B cell receptors with ultralong complementarity determining regions 3 (CDR3). Antibodies with these specialized structures have superior virus neutralization characteristics. Published studies of B cell receptors with ultralong CDR3s in dairy cattle have been limited by the number of animals examined (1-4 animals in each study), and by varying breeds and ages. The objective of this study was to assess the percentage of IgM and IgG sequences with ultralong CDR3s, and gene usage in blood and colostral lymphocytes from cows classified as high, average, and low immune responders based on their estimated breeding values. B lymphocytes were isolated from the blood of 14 heifers and 7 cows. In addition, cells were isolated from colostrum of the 7 cows. RNA was extracted, cDNA was produced, and IgM and IgG transcripts were amplified using polymerase chain reactions. Amplicons were sequenced using Oxford Nanopore long-read sequencing. In sequences derived from blood B cells, AMIR estimated breeding values were significantly and positively associated with higher percentages of IgG ultralong CDR3 sequences. High AMIR cows (n = 3) also produced colostrum with a significantly greater percentage of IgG ultralong CDR3 sequences (18.0 %) than average AMIR cows (n = 4, mean 8.8 %). Larger studies are needed to investigate the association between percentages of B cells expressing IgG ultralong CDR3s and observed health traits.