Furthermore, GCs were small and loosely organized in the spleen of WT mice prior to and after re-infection, although they became larger and more organized by day 35 p.c. In contrast, GCs were not present in the spleen before or after re-challenge of Icos-/- mice, suggesting that Ab production was mediated through the extrafollicular response after re-challenge. The gene discussed is ICOS; the disease is infection.