The role of humoral and cellular mediators in enhanced mammary inflammatory reactions to staphylococcal infection in systemically immunized ewes

Prior systemic immunization with live Staphylococcus aureus vaccine enhances the early recruitment of neutrophils into nonlactating mammary glands infected with staphylococci. The study investigates the role of humoral and cellular mediators in this phenomenon. Intramammary infusion of bacteria suspended in immune sheep serum did not enhance the inflammatory response to infection in nonimmunized ewes despite the presence of complement in the infused serum. Infusion of complement activated by incubation with zymosan evoked a massive neutrophil influx into mammary secretions by 4 hr after infusion. Hemolytic complement activity was not detected in mammary secretions of immunized or nonimmunized ewes. These findings indicate that, despite the inflammatory effect of complement activation, humoral immune factors did not promote neutrophil migration into infected glands. Mammary glands of systemically immunized ewes stimulated 5 days previously with staphylococcal soluble antigens (SSA) supported larger neutrophil influxes during staphylococcal infection than contralateral glands stimulated with endotoxin 5 days prior to infection. Exudates of SSA‐stimulated glands had significantly higher cell concentrations, prior to infection, than endotoxin‐stimulated glands; however elevated cell concentrations in endotoxin‐stimulated glands of nonimmune ewes did not support enhanced inflammatory responses. These findings suggest that qualitative but not quantitative characteristics of mammary leucocytes influence the inflammatory response to infection in systemically immunized ewes

The Effect of Systemic Treatment with Platelet-Activating Factor on the Migration of Eosinophils to Lung, Pleural and Peritoneal Cavities in the Guinea Pig

Subcutaneous treatment of guinea pigs with platelet-activating factor (PAF) caused an increase in the prevalence of eosinophils in lavage fluid recovered from pulmonary airways, and pleural and peritoneal cavities. In PAF-treated animals, total numbers of eosinophils and macrophages in washings were positively correlated, thus there was no apparent competition between the two cell types for migration at traffic sites into body cavities. The results indicate that PAF acts centrally to enhance the migration of eosinophils and monocytes into body cavities, perhaps by inducing bone marrow release of both classes of leucocytes which may then migrate constitutively into lung, pleural and peritoneal cavities.</jats:p

Using immunology and resistant sheep to beat the fly

New methods for controlling blowfly strike will be needed when mulesing is phased out and the availability or efficacy of insecticides for control of fly strike decreases. The Australian Sheep Industry CRC has pursued two approaches for the development of new methods to help control blowfly strike. In the first, genetic resistance of sheep to survival and growth of blowfly larvae was examined. Resistance to growth of larvae was heritable (0.29 ± 0.22). The trait was not associated with resistance to internal parasites, nor was it influenced by wool characteristics such as fibre diameter or coefficient of variation of fibre diameter. This new trait differs from resistance to fly strike associated with resistance to fleece rot. Because measurement of the trait is labour intensive, gene markers or correlated measures are needed before it will be suitable for industry adoption. The second approach examined the impact of larval products on the immmune system of the sheep. Larvae suppress the sheep immune system and thereby limit the ability of the sheep to reject the larvae. The immunosuppresive agent is being purified and strategies to abolish its activity are being explored. Abolition of immunosuppression would create opportunities for the development of new vaccines againts blowfly strike