Cortisone-induced immunotolerance to nematode infection in CBA/Ca mice. I. Investigation of the defect in the protective response.

The parasitic nematode Trichuris muris is expelled from the large intestine of CBA/Ca mice after approximately 20 days of infection. Short term treatment with cortisone acetate prevented expulsion and allowed the establishment and survival of an adult worm population for at least 70 days. This tolerance to the primary infection persisted after removal of the adult worms by chemotherapy and allowed the full development of a secondary infection. High levels of blast activity were seen in the mesenteric lymph node on days 30 and 40 of a primary infection in tolerant mice. Serum taken from tolerant mice passively conferred immunity on naive mice, but cells transferred from such donors were ineffective. Cells from immune mice were not capable of eliciting expulsion of an established primary infection in tolerant mice but did cause a significant reduction in worm numbers when given on the same day as a secondary infection. Cells from naive mice had no effect upon infections in tolerant mice. It is suggested that, in this system, corticosteroid treatment deletes an accessory cell population causing tolerization of immunocompetent T cells.