Figure 3.

Respiratory syncytial virus (RSV)–induced plasmablast expansion correlates with IgG and IgA increment. (A) Antigen-specific antibody (Ab)-secreting cells (ASCs) were enumerated using B-cell enzyme-linked immunospot with whole RSV lysate where sufficient peripheral blood mononuclear cells (PBMCs) were available. Uninfected (polymerase chain reaction–negative) subjects (n = 12) are shown in blue, infected (polymerase chain reaction–positive) subjects (n = 16) in red. (B) Peak antigen-specific ASC frequencies as percentage of total immunoglobulin-positive cells for infected subjects. Horizontal bars indicate the median. (C) Correlation of fold change in serum neutralizing Ab with peak IgG⁺ ASC frequency. (D) Correlation of fold change in nasal IgA against RSV with peak IgA⁺ ASC frequency (data from 27 subjects; nasal IgA in one subject could not be measured). (E) Correlation of peak ASC frequency with preinfection baseline serum neutralizing Ab titers. ASC frequencies are expressed as log₁₀ per million PBMC. P values for unpaired Mann-Whitney Wilcoxon U tests and/or Spearman rank correlation coefficient (R_s) are shown as appropriate. Open circles = uninfected subjects; solid circles = infected subjects. Ab = antibody; EC₅₀ = half-maximal effective concentration. ns = P > 0.05; *P < 0.05; **P < 0.01; ***P < 0.001.