Differential TCR gene usage between WC1- and WC1+ ruminant γδ T cell subpopulations including those responding to bacterial antigen

Ruminant gamma delta T cells are divided into subpopulations based on the presence or absence of WC1 co-receptors (scavenger-receptor-cysteine-rich family members uniquely expressed on gamma delta T cells). Evidence suggests WC1(+) are inflammatory while WC1(-) are regulatory and that they also differ in their tissue distribution. Recently, this paradigm was refined further as cells that produce interferon-gamma and proliferate to autologous antigens, leptospira antigens, or IL-12 were largely found within the WC1(+) subpopulation that bears the WC1.1 antigenic epitope but not that bearing the WC1.2 epitope. Here, the T cell receptor gene expression by these different subpopulations (WC1(-), WC1.1(+), and WC1.2(+)) was compared using flow cytometrically-purified cells and reverse transcriptase-polymerase chain reaction (RT-PCR). The WC1(-) gamma delta T cells had transcripts for all 11 possible combinations of the TRG subgroup V and C genes while those in both WC1(+) subpopulations were restricted to TRGV3-TRGC5 and TRGV7-TRGC5. In contrast, all three subpopulations expressed transcripts from all four known bovine TRDV genes. Further analysis of the WC1(+) gamma delta T cells that proliferated in leptospira antigen-stimulated cultures indicated that they do not represent a unique subpopulation within the larger WC1(+) population based on their TCR gene usage. Moreover, sequencing of 65 transcripts showed that their junctional regions were diverse as TRGJ5-1, TRGJ5-2, TRDJ1, and TRDJ3 were used, and CDR3s ranged from 9 to 24 amino acids. The restricted but shared gamma delta TCR gene usage for WC1.1(+), WC1.2(+), and WC1(+)-antigen-responsive cells leaves open the possibility that the WC1 co-receptor is an important determining element in the activation process and subsequent response.