Blockade of ICOS and IL-27R by administration of antibodies from day −1 of infection did not substantially alter the frequencies of total antigen-experienced (CD11a+ CD49d+) CD4+ or CD4+ YFP+ T cells in any examined organ, indicating that neither ICOS nor IL-27R is important for development of the proinflammatory parasite-specific CD4+ T cell response during infection (results not shown). The gene discussed is ICOS; the disease is infection.