Furthermore, no statistical differences were found in the magnitude of cellular response to M or N proteins according to past infection (convalescents) or infection-naive individuals with cross-reactive cellular immunity, either in CD8 (p = 0.618 and p = 0.750, respectively) or CD4 (p = 0.591 and p = 0.636, respectively) cell responses (Figures 4, 5, respectively). Here, CD4 is linked to infection.