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 suc h as the nature and quantity of the pathogen, the route of infection, the i nfluence of immunomodulatory components and of concomitant infections, as w ell 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 cyt okine environment of the T cells during and following activation. Understan ding how such factors influence immune class regulation is fundamental to u nderstanding the pathology of infectious diseases. Curr Opin infect Dis 13: 209-213. (C) 2000 Lippincott Williams & Wilkins.