Modulation of nasopharyngeal innate defenses by viral coinfection predisposes individuals to experimental pneumococcal carriage

Glennie, S; Gritzfeld, J F; Pennington, S H; Garner-Jones, M; Coombes, N; Hopkins, M J; Vadesilho, C F; Miyaji, E N; Wang, D; Wright, A D; Collins, A M; Gordon, S B; Ferreira, D M

We investigated whether anti-PspC antibodies purified from individuals participating in the EHPC model could block FH binding to pneumococcus in vitro and circumvent the increased adherence of pneumococcus during inflammation. The specific binding of FH via PspC to our laboratory strain was confirmed (Supplementary Figure S1A ,B online). Anti-PspC antibodies were isolated from serum where they are more abundant than in nasal wash. Flow cytometric analysis indicated that samples from each subject had anti-PspC IgG that bound effectively to pneumococcus (Figure 4a, P ¼ 0.01 using unpaired t-test). Levels of IgG binding were variable among samples and related to anti-PspC IgG levels measured by enzyme-linked immunosorbent assay (ELISA; Supplementary Figure S1C ). Purified samples also had measurable levels of FH remaining after the anti-PspC IgG purification process (Supplementary Figure S1C ). Purified samples were incubated with bacteria before addition of FH in order to block PspC-FH interaction. We observed a partial inhibition of FH binding to pneumococcus by purified human anti-PspC IgG samples ( Figure 4b) .