Figure 4. Role of CD4+ T lymphocytes in vaccine based protection against heterologous or homologous serotype strains.
Proliferation of splenic T cells from vaccine immunized mice compared with that of unimmunized mice after the stimulation for 24 h (A) and 72 h (B) by heat-killed, whole bacterial cell antigen (ATCC 27853, PAO- and PAO-6). Immunized T cells have higher proliferation than the controls when stimulated by targeted cells at both time points, and the proliferation was significantly decreased by anti-CD4 antibody instead of CD8 antibody. Cells were pooled from three to five mice per group. Results were shown as mean ± SD (ANOVA, n = 3, *p < 0.05, **p < 0.01); Mice of control group were immunized with NS, and experimental groups were immunized with escalating doses of 108, 5 × 108, 109 and 5 × 109 CFUs irradiated ATCC 27853 cells every week. At the same time, mice were given either anti-CD4 monoclonal antibody (GK1.5), anti-CD8 monoclonal antibody (clone 2.43) or normal rat IgG to deplete CD4 and CD8 lymphoctyes, and then were challenged with 5 × 106 CFUs the parental strain ATCC 27853 (C), 5 × 106 CFUs homologous serotype PAO-1 (D) and 1 × 107 CFUs heterologous serotype PAO-6 (E). Kaplan–Meier curves were plotted, and depletion of CD4+ T lymphocytes showed complete abrogation of the anti-infectious activity with the immunization, whereas depletion of CD8+ T lymphocytes did not affect the protective immunity (n = 10, *p < 0.05, **p < 0.01).