1a.Objectives (from AD-416):
Objective 1- identify ligands from mycobacteria that bind WC1+ bovine T cells by expressing each of the bovine SRCR domains from CD163 family members (WC1, CD163 molecules) - ligands may be detected in antigen fractions containing secreted products or surface ligands of the bacteria.
Objective 2 - produce transfected cells expressing SRCR domains that have pathogen binding capabilities into mononuclear cells to evaluate affects on in vitro specific immune responses.
Objective 3 - evaluate cells and tissues from M. bovis infected and BCG vaccinated cattle to determine if cells expressing WC1 or CD163 molecules increase in number and responsiveness upon infection/vaccination.
1b.Approach (from AD-416):
Our labs have shown that bovine gamma delta T cells expressing the immune co-receptor WC1 (WC1+ gamma delta T cells) are activated in response to Mycobacterium and Leptospira. WC1 is part of the scavenger receptor family known as CD163 which includes CD163A, CD163b and CD163c-a in humans. The mechanism of activation of gamma delta T cells in all mammalian species including humans via the gamma delta T cell receptor (TCR) and co-receptors remains largely enigmatic. However we have previously shown that the cell surface glycoproteins belonging to the WC1 family of receptors act as activating co-receptors in conjunction with the TCR. The bovine genome contains approximately fourteen WC1 genes and we have shown that two of these WC1 gene products contribute to the bovine gamma delta T cell response to Leptospira; another two have been implicated in the bovine gamma delta T cell response to Anaplasma by others. We hypothesize that specific domains of CD163/WC1 gene products bind various bacteria and their products and once elucidated can be exploited to develop vaccines in both species (humans and cattle).
Bovine tuberculosis is caused by Mycobacterium bovis (M. bovis), a zoonotic pathogen that causes a chronic infection in cattle, despite eliciting a robust and specific immune response. Gamma delta T cells are a poorly understood, yet large subpopulation of white blood cells in cattle that contribute to immune responses. The objective of this project is to characterize the gamma delta T cell response to M. bovis infection of cattle and to determine the function of surface molecules on these cells. Studies conducted this year demonstrated that peripheral blood gamma delta T cells of cattle respond robustly to both protein and non-protein mycobacterial antigens. We observed responses by gamma delta T cells to targets that are also known to induce responses in other T cells and observed significant interferon-gamma production to mycobacterial components by both mixed white blood cell populations and purified gamma delta T cells. Future studies will work at identifying the gamma delta T cell subsets that localize to the lungs and draining lymph nodes of cattle infected with M. bovis, and characterizing immune responses of these cells to tuberculosis antigens. Understanding how gamma delta T cells respond to infection with M. bovis may provide insights into potential methods for controlling tuberculosis (e.g., vaccination), that may also be translatable to other zoonotic pathogens (e.g., Leptospirosis, Brucellosis).