CD4 and infection: Furthermore, when considering all patients, regardless of post-infection timing, specific IgG titers were positively correlated with the percentages of CD25+ CD134+ CD4 T-cells responding to N (r = 0.4285, p < 0.0001) and S proteins (r = 0.4706, p < 0.0001), but also with their respective stimulation indexes (N: r = 0.3755, p = 0.0024; S: r = 0.4007, p = 0.0011).