Ovalbumin-specific plasma cell numbers detected at the peak of the secondary response strongly correlates with ovalbumin-specific IgG titres detected up to 5 months post-boost immunisation. Pearson's correlation coefficient (r) was determined to examine the association between the Log₁₀ anti-ovalbumin IgG titres and the Log₁₀ memory B cell (A) or plasma cell (B) numbers detected at the peak response following the boost-injection of ovalbumin (day 17 pb, day 6 pb and day 4 pb, respectively). A similar analysis was performed to examine the association between the Log10 anti-ovalbumin IgG titres detected 5 months later and the Log10 memory B cell (C) or plasma cell (D) numbers detected at the peak response (day 6 pb and day 4 pb, respectively); pb: post-boost.