Delayed-type hypersensitivity in mice immunized with Trypanosoma rhodesiense antigens.

When mice were immunized intravenously, subcutaneously, or by the footpad route with formaldehyde-killed Trypanosoma rhodesiense, delayed-type hypersensitivity was elicited by the use of frozen-thawed trypanosomal antigen. The delayed footpad swelling technique was used to measure delayed hypersensitivity. Hypersensitivity induction was dose dependent (greater than or equal to 10(6) formaldehyde-treated T. rhodesiense) and was affected by the route of immunization. The footpad route induced higher levels of hypersensitivity than other routes of immunization. Mice immunized with a single dose of formaldehyde-treated antigen and challenged with live T. rhodesiense did not survive. Yet, mice immunized subcutaneously with formaldehyde-treated antigen and then injected with frozen-thawed antigen and challenged 28 days after immunization survived. The results suggest that T-cell activation, manifested by delayed hypersensitivity responses, was a necessary component in the protective response, perhaps functioning in a helper cell capacity.