Pathogenetic mechanisms in immune polioencephalomyelitis: induction of disease in immunosuppressed mice

Immune polioencephalomyelitis (IPE) was induced by the i. p. injection of x-irradiated (10,000 R) syngeneic line I/sub b/ malignant lymphocytes into C58 mice that were 7 or more months old and in young mice immunosuppressed by x-ray or drugs. The occurrence of IPE in young immunosuppressed C58 mice was systematically analyzed. When mice less than 2 weeks old were x-irradiated with 600 R, IPE could not be induced. The incidence in 1-month-old mice was approximately 50 percent and increased progressively with the age except for a drop in incidence at 3 months. An analysis of the dose effects of x-irradiation on the occurrence of IPE in mice of different ages revealed a marked increase in the incidence in 3- and 5-month-old mice beginning at dose levels of 450 R and 300 R, respectively. Considered together, these data indicated that two sub-populations of immunocytes differing in x-ray sensitivity interacted to protect mice from IPE. It appears that under natural conditions an x-ray sensitive cell population, possibly having suppressor function, decreased with age and made mice susceptible to induction of IPE. Five-month-old mice were immunosuppressed with an LD10 of cyclophosphamide, prednisolone, or methotrexate to determine whether mice immunosuppressed with drugs also were susceptible to the induction of IPE