The use of somatic antigen of Haemophilus influenzae for the monitoring of T cell-mediated skin test reactivity in man.

To investigate its usefulness as a skin test antigen, Haemophilus influenzae somatic antigen was tested in 28 healthy individuals, both in soluble and aggregated form. All subjects were found to possess specific antibodies against H. influenzae of both IgG and IgM subclass, thus showing their previous exposure to this commensal micro-organism. The somatic antigen in solution was found to be a poor antigen for eliciting a delayed hypersensitivity skin response: only 2 out of 16 subjects reacted with a positive DTH pattern. In contrast, 25 out of 28 persons showed a positive DTH pattern when somatic antigen was used in aggregated form. Two types of DTH reaction patterns could be detected (in a ratio of approximately 3:2), viz. those with an early (24 h) and those with a late (48 h) maximal swelling. Histology of 3 early and 1 late DTH reaction showed perivascular infiltrates of mainly Thelper/Tinducer lymphocytes. Hardly any basophils were seen. One negative skin test, biopsied at 6 h, showed no signs of Arthus reactivity. It can be concluded that skin tests using the aggregated form of the somatic antigen of H. influenzae are useful for assaying specific T-cell-mediated reactivity in man.