We have demonstrated that subcutaneous immunization of rats with heath killed cells of Cryptococcus neoformans (HKC) emulsified in complete Freund adjuvant (CFA), 4 days before C. neoformans infection; provides host protection against disseminated cryptococcosis. The focus of this study was to evaluate the mechanisms of the immune response involved in this phenomenon. Four days after immunization of Wistar rats with HKC-CFA, nitric oxide (NO) and hydrogen peroxide (H₂O₂) production was detected by colorimetric methods in cultures of peritoneal (PC) and spleen (spm) cells. Proliferative response to HKC was measured by [³H]thymidine incorporation into DNA, and intracellular cytokine synthesis and ED₂ surface expression was evaluated by flow cytometry in spm cells. Peritoneal and spm cells of HKC-CFA immunized rats produced higher NO and H₂O₂ levels than those produced by cells from CFA immunized rats (NO: PC, p<0,008; spm, p<0,002; H₂O₂: PC, p<0,030; spm, p<0,015). In addition, we observed that immunization with HKC-CFA resulted in an increment of the number of CD4⁺ cells producing INF gamma (p<0,011) and the percentage of ED2 positive cells compared to control rats. Moreover, HKC-CFA immunized rats showed higher specific lymphoproliferation than CFA immunized animals (p<0,020). In conclusion, our results indicate that immunization with HKC-CFA is able to induce CD4⁺ cells producing INF-gamma as early as 4 days post-immunization, and to activate macrophages with production of microbicidal molecules. Those are important mechanisms involved in protection against C. neoformans infection.