IMMUNE MODIFICATION OF THE PATHOGENESIS OF STREPTOCOCCUS-UBERIS MASTITIS IN THE DAIRY-COW

Two groups of 4 cows were vaccinated subcutaneously with live Streptoc occus uberis strain 0140J or a surface extract derived from the same s train, at 14 days prior to the cessation of lactation (drying off) and at calving. Both groups also received an intramammary administration of the surface extract 7 days after drying off. A third group of unvac cinated animals acted as controls. Following intramammary challenge of two quarters per cow with the vaccine strain, all quarters on control cows and those vaccinated only with surface extract developed clinica l mastitis. However, only 12.5% of challenged quarters on cows which w ere vaccinated with live bacteria developed clinical mastitis. In addi tion, the numbers of bacteria in the milk following challenge were 10( 5) times higher from the control and extract vaccinated cows than thos e which received live vaccine. Serum levels of S. uberis specific IgG, were elevated in the animals vaccinated with the live organism when c ompared to that of either extract-vaccinates or controls, whilst S. ub eris specific levels of IgG(1) and IgM were similar in all groups thro ughout the experiment. Specific antibody levels in milk were unaffecte d by vaccination. Despite increased levels of IgG(2), no increase in o psonic activity was detected in any serum or milk samples. Peripheral blood lymphocytes from animals vaccinated with live organisms showed a considerable increase in proliferative response to S. uberis antigen in vitro when compared with lymphocytes from control and extract-vacci nated animals. These results suggest that neutrophils and specific ops onising antibody may not form the major defence against infection with S. uberis.