Figure 4.

Antigen-specific IgG⁺ memory B cells (MBC) are induced by respiratory syncytial virus (RSV) infection. Peripheral blood mononuclear cells (PBMCs) were obtained on Days 0 and 28 postinoculation and MBCs polyclonally activated. Total and antigen-specific immunoglobulin-producing cells were then enumerated using enzyme-linked immunospot. (A) Antigen-specific IgG⁺ MBC frequencies for uninfected (open circles) versus infected (solid circles) subjects at baseline and Day 28 postinoculation (infected only). P > 0.05 for all comparisons except where shown. MBC frequencies are expressed as percentage of total immunoglobulin-positive cells. Horizontal bars indicate the median. (B) Fold change (log₂) of IgG⁺ MBCs postinfection compared with baseline for infected subjects (n = 17). Horizontal bars indicate the median. (C) Correlation between peak acute antibody-secreting cell (ASC) frequency at Day 10 and fold change over baseline (log₂) of RSV-specific IgG⁺ MBC. Spearman rank correlation coefficient (R_s) or P values for unpaired Mann-Whitney Wilcoxon U test are shown as appropriate. FP = purified RSV fusion protein; MV = measles virus; RSV = whole RSV. ns = P > 0.05; *P < 0.05; **P < 0.01; ***P < 0.001.