The use of a pan-IGHG reverse primer allowed amplification of any IgG isotypes, and sequence analysis revealed the use of IGHG1, IGHG3, and IGHG5 isotypes in foals, and IGHG1 and IGHG6 in mares for both KLH- and influenza-specific B cells. The gene discussed is IGHG3; the disease is influenza.