Protective antibodies in infections with Eimeria maxima: the reduction of pathogenic effects in vivo and a comparison between oral and subcutaneous administration of antiserum

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Abstract
Crude globulin fractions were prepared from the pooled serum of chickens 14 days after their inoculation with oocysts of Eimeria maxima (‘immune’ globulin) and from the pooled serum of similar but coccidia-free chickens (‘normal’ globulin). The fractions were injected subcutaneously into young chicks which were challenged with large numbers of oocysts and whose weight gains over the next 7 days were measured. The weight gains in all infected groups of chicks were lower than in uninfected and uninjected controls, but the gains in groups of chicks injected with ‘immune’ globulin preparations were higher than in groups given ‘normal’ globulin. Oocyst production in the groups given ‘immune’ globulin was very much lower than in the control groups, untreated or given ‘normal’ globulin.The reduction of oocyst production by antisera given by the subcutaneous and oral routes was compared. The weaker of two antisera had no effect when given orally but caused some reduction in oocyst numbers when given subcutaneously. A stronger antiserum produced some effect when given orally but was considerably more protective when given subcutaneously. The findings are discussed in relation to the mode of action of antibodies in protecting against infection.