Factors that influence T helper cell response to infection

Many factors influence the decision of a precursor T helper cell to become either a type 1 or type 2 cell. These comprise pathogen-defined factors such as the nature and quantity of the pathogen, the route of infection, the influence of immunomodulatory components and of concomitant infections, as well as host-defined factors including genetic predisposition, the number of responding T cells, the major histocompatibility complex haplotype of the individual, the nature of the antigen presenting cells involved and the cytokine environment of the T cells during and following activation. Understanding how such factors influence immune class regulation is fundamental to understanding the pathology of infectious diseases.