Relationship between age and cellular suppressive activity in resistance to Histoplasma capsulatum infection.

One-month-old and 1-year-old male BALB/c mice showed a lower resistance than 4.5-month-old mice to Histoplasma capsulatum infection. 4.5-month-old mice successfully resolved the infection when challenged with either a LD50 or LD100 for 1-month-old mice. A critical clinical course of experimental histoplasmosis was observed in 4.5-month-old syngeneic mice when spleen cells from 1-month-old BALB/c mice were transferred to them. Irradiated recipient mice, into which bone marrow and spleen cells were transferred, died when infected with the LD100 for 1-month-old mice. The same occurred with 4.5-month-old non-irradiated infected mice which received only spleen cells and with 1-month-old mice which were used as a control of infection. However, infected and non-transferred 4.5-month-old mice survived this dose. Thus, the adoptive transference of spleen cells from 1-month-old mice to 4.5-month-old mice suppressed the resistance of these adult mice to infection. Apparently, the transference of the suppressive state requires the presence of two cell populations, a non-adherent and an adherent and radioresistant cell present in the spleen of male 1-month-old mice.