Passive transfer of maternal immunoglobulin isotype antibodies against tetanus and influenza and their effect on the response of foals to vaccination

Influenza and tetanus-specific antibodies of the IgG sub-isotypes are posiv ely transferred to foals via colostrum and inhibit their response to inacti vated influenza vaccines and tetanus toxoid. High titres of influenza antib odies of IgGa and IgGb subisotypes and tetanus antibodies of the IgGa, IgGb and IgG(T) subisotypes were detected in postsucking serum samples collecte d from foals born to mares that had received booster doses of multicomponen t vaccines during the last 2 months of gestation. Thereafter, titres declin ed in an exponential manner but were still detectable in all foals at age 2 6 weeks, regardless of whether they had been vaccinated prior to age 26 wee ks. Mean +/- s.e. half-life of decline of influenza IgGa antibodies (27.0 /- 2.3 days) was significantly shorter than that of influenza IgGb antibodi es (39.1 +/- 2.7 days; P <0.005). Tetanus IgGa and IgGb antibodies declined with half-lives of 28.8 +/- 3.0 and 34.8 +/- 5.1 days, respectively. Titre s of tetanus IgG(T) antibodies were substantially higher than those of infl uenza IgG(T) antibodies in postsucking samples and remained so through age 26 weeks, declining with a half-life of approximately 35 days. Postsucking titres of tetanus and influenza antibodies of the IgA isotype were low and declined rapidly to undetectable levels. Yearlings showed significant increases in titre of influenza IgGa, IgGb and IgG(T) subisotype antibodies but no increase in influenza IgA antibodies i n response to 2 doses of multicomponent vaccines containing tetanus toxoid and inactivated influenza A-1 and A-2 antigens. Yearlings also showed stron g tetanus IgGa, IgGb and IgG(T) subisotype responses to one dose of vaccine and a substantial further rise in titre in response to administration of a second dose 3 weeks later, but failed to show an increase in titre of teta nus IgA antibodies. The influenza and tetanus IgGa, IgGb and IgG(T) subisot ype responses of 6-month-old foals to vaccination followed the same pattern as those shown by yearlings but titres were generally lower. In contrast, 3-month-old foals failed to show increases in titre of either influenza or tetanus IgG subisotypes in response to 2 doses of vaccine and generally nee ded 1-3 additional booster doses of vaccine to achieve titres similar to th ose achieved by yearlings after 2 doses. Based on the finding that maternal antibodies exert a significant inhibitory effect on the response of foals to tetanus toxoid and inactivated influenza antigens, it is recommended tha t primary immunisation of foals born to vaccinated mares should not commenc e before age 6 months.