CD4+ T Cell Responses to Pathogens in Cattle

Abstract

Helper CD4+ T cells are essential in shaping effective antibody response and cytotoxic T cell response against pathogen invasion. There are two subtypes of pathogen-specific helper T cells in mice and humans; type 1 (Th1) and type 2 (Th2), with Th1 producing interferon-gamma (IFNγ) and Th2 producing interleukin-4 (IL-4). While effective Th1 controls intracellular pathogens like viruses, efficient Th2 controls extracellular pathogens like most parasites. However, the most predominant CD4+ T cell subtype in cattle is Th0, which produces both IFNγ and IL-4, and only exists in small amounts in mice and humans. Moreover, in many bovine infections, both IFNγ and IL-4 were detected in the blood and both antigen-specific IgG2 (Th1 associated bovine antibody) and antigen-specific IgG1 (Th2 associated bovine antibody) were upregulated in the serum, suggesting bovine CD4+ T cell responses may vary from those in mice and humans. How bovine CD4+ T cell differentiation differs from that in mice and humans and how some critical bovine pathogens regulate immunity to establish chronic infections are largely unknown. This chapter summarizes current literature and identifies the knowledge gaps to provide insights into future research in the field.