Induction of milk IgA antibodies by porcine respiratory coronavirus infection.

An ELISA was developed to examine the prevalence of TGEV-specific immunoglobulin (Ig)A in the milk of sows, infected in the field with PRCV or with TGEV. It was shown that previous PRCV-infections can induce the secretion of IgA antibodies in the milk. However, only 9 out of 28 PRCV-infected sows had IgA in their milk whereas 11 TGEV-infected sows all secreted IgA. On farms where a reinfection with PRCV occurred, the number of IgA-secreting sows increased from 2 to 11 on a total of 13 sows. This showed that the presence of IgA antibodies in the milk may depend upon the occurrence of reinfection with PRCV. As demonstrated by density gradient analysis, the milk IgA induced by PRCV was 11S secretory IgA and had the capacity to neutralize TGEV.