Phytohemagglutinin skin test responses to evaluate in vivo cellular immune function in rats

It is often necessary to have a small animal model which permits the sequential evaluation of functional immune status over a period of time. We report here the in vivo, intradermal response to phytohemagglutinin which produces an area of induration that is histologically similar to a typical delayed cutaneous hypersensitivity response, and that provides fast, quantitative, reproducible results similar to those observed with standard but more laborious and variable in vitro tests of immune function. For small animal studies this has the advantage of permitting longitudinal evaluations over time without sacrificing the animal. Using phytohemagglutinin-microprotein (0.2 mg/0.1 ml), injected intradermally, a delayed cutaneous hypersensitivity-like response is induced which is maximal at 24 hr. When immune function was altered either by treatment with a chemical immunosuppressant (ethanol) or by hormonal manipulations (hypophysectomy and rat growth hormone), the delayed cutaneous hypersensitivity-like response (area of induration) correlated closely with both macrophage migration inhibitory factor changes (r = 0.98; P less than 0.001) and mixed lymphocyte reaction changes (r = 0.99; P less than 0.05). These observations suggest that this technique correlates well with standard in vitro measures of immune response and may thus permit an in vivo estimation of immune reactivity.