ANALYSIS OF THE IMMUNE-RESPONSE IN SHEEP EFFERENT LYMPH DURING SALMONELLA-ABORTUSOVIS INFECTION

The efferent lymph duct of the ovine prescapular lymph node was cannul ated, and Salmonella abortusovis (SAG), a specific pathogen for sheep inducing abortion and mortality of newborn lambs, was inoculated by th e subcutaneous route in this lymph node drained area, While the presca pular lymph node draining the inoculation site represented an efficien t barrier for the vaccinal SAO Rv6 strain spreading, SAO 15/5 virulent bacteria were steadily detected in efferent lymph of infected sheep. The inoculation of the virulent strain of SAO induced a greater increa se of the cell output than did the attenuated vaccinal strain, but pro portions of blast cells appearing in the efferent lymph were similar i n both cases. Flow cytometry analysis showed that B and T cell outputs were both increased during SAO infections, but while T cell subset pr oportions slightly decreased, B cell percentages significantly rose, a nd, at the peak response, almost all of the lymphoblast cells were act ivated B cells. Typical antibody profiles characteristic of a primary immune response were observed, and antibody titres were greater in the efferent lymph of animals inoculated with the virulent strain of SAG. Many of the cytokine mRNAs we investigated were steadily detected by RT-PCR in efferent lymph cells of control sheep, but frequencies of de tection of IL-2, IFN gamma, IL-1 beta and TNF alpha mRNAs were augment ed in efferent lymph cells following inoculation of both SAO virulent or vaccinal strains. IL-10 and IL-8 mRNAs could only be detected after a SAO inoculation, while detection of IL-4 mRNAs was increased only i n efferent lymph cells from SAO virulent strain-infected sheep. The ef ferent lymph cannulation technique thus appeared a very powerful way t o study the in vivo development of the immune response to SAG, in its natural host, the sheep. (C) 1997 Elsevier Science B.V.