The virus-neutralizing Ab titer was calculated as the highest dilution yielding less than 50% cytopathic effect. Rhein-8-O-beta-D-glucopyranoside approximately 18-fold lower titers of Ab against surface antigens ofM. haemolyticaand approximately 20-fold lower titers of leukotoxin-neutralizing Abs than domestic lambs. The titers of leukotoxin-neutralizing Abs in the serum and colostrum samples of BH ewes were approximately 157- and 50-fold lower than those for domestic ewes, respectively. Comparatively, the higher titers of parainfluenza 3 virus-neutralizing Abs in the BH lambs ruled out the possibility that these BHS had an impaired ability to passively transfer Abs to their lambs. These results suggest that lower levels of leukotoxin-neutralizing Abs in the sera of BH ewes, and resultant low Ab titers in their lambs, may be a critical factor in the poor lamb recruitment in herds affected by pneumonia. == INTRODUCTION == The bighorn sheep (BHS;Ovis canadensis) population of North America has declined from an estimated 2 million animals at the beginning of the 19th century to less than 70,000 at this time (2,32). Factors contributing to this population decline include predation, loss of habitat, competition for forage with livestock, and respiratory disease. Outbreaks of bronchopneumonia in previously healthy populations of BHS often result in high death rates among all age groups initially, followed by years of impaired recruitment due to pneumonia in lambs (5,21,24,28). During these outbreaks, members of the generaMannheimia,Bibersteinia, andPasteurella, includingMannheimia(Pasteurella)haemolytica,Bibersteinia(Pasteurella)trehalosi, andPasteurella multocida, have commonly been isolated from pneumonic lungs (16,26). Of these,M. haemolyticahas consistently been shown to cause fatal bronchopneumonia in BHS under experimental conditions (9,12,20). WhileM. haemolyticacan cause pneumonia in multiple ruminant species, including cattle and domestic Rhein-8-O-beta-D-glucopyranoside sheep (DS), BHS are particularly susceptible to this disease. A number of studies have shown that BHS demonstrate greater susceptibility toM. haemolytica, and exhibit more severe pathology when infected, than DS (9,11,12,24). There is evidence for a protective role for antibodies (Abs) against surface antigens ofM. haemolyticaand its virulence factors, as vaccines containing these antigens and the exotoxin (leukotoxin [Lkt]) produced by this organism have conferred protection against experimental challenge (3,19,22,30). High titers of Lkt-specific Abs also reduced the risk of pasteurellosis in cattle infected either experimentally or naturally (7). Furthermore, administration of immunoglobulins (Ig) from immune Rhein-8-O-beta-D-glucopyranoside sheep to lambs resulted in protection against experimentalM. haemolyticachallenge (18). In ruminants, due to the syndesmochorial nature of the placenta, maternal Abs are not transferred to the offspringin utero(25). In neonatal ruminants, the transfer of maternal Abs occurs via colostrum during the first 24 h of life. This transfer of maternal Abs via colostrum is critically important for immunologic protection of neonatal ruminants as their immune systems become fully competent. Failure of passive transfer may occur at multiple levels, including insufficient concentration of Ig in the colostrum due to lack of specific pathogen exposure or an inability to respond, insufficient intake of colostrum by the neonate, or inefficient transfer of Ig from the neonatal intestine to blood. Failure of passive transfer has been associated with multiple diseases of ruminant neonates, including respiratory disease, diarrhea, septicemia, and omphalophlebitis (13,14). The poor lamb recruitment observed in BHS herds following outbreaks of pneumonia, and the importance of Abs in protection againstM. haemolytica-caused pneumonia, prompted us to hypothesize that BH lambs receive lower levels ofM. haemolytica-related Abs from their dams than domestic lambs. Therefore, the objective of this study was to determine the titers of Ab againstM. haemolyticasurface antigens and Lkt in the sera of lambs from these two species at birth and weekly for 12 weeks. == MATERIALS AND METHODS == == Materials. == Rabbit anti-sheep IgG conjugated to horseradish peroxidase and the ABTS [2,2-azinobis(3-ethylbenzthiazolinesulfonic acid)] substrate system were purchased from KPL (Gaithersburg, MD). PRO-BIND 96-well enzyme-linked immunosorbent assay (ELISA) plates were purchased from Becton Dickinson (Franklin Lakes, Rabbit Polyclonal to SPHK2 (phospho-Thr614) NJ). The MTT (3-[4,5-dimethylthiazoyl-2-yl]-2,5-diphenyl tetrazolium bromide) Rhein-8-O-beta-D-glucopyranoside dye ando-phenylenediamine were purchased from Sigma Aldrich (St. Louis, MO). Colorless RPMI 1640 was purchased from Invitrogen (Carlsbad, CA). Immulon IB plates were purchased from Dynatech Laboratories (Alexandria, VA). == Sample collection and processing. == Serum samples were collected via venipuncture from 12 domestic ewes and 12 BH ewes (DS herd 1 and BHS herd 1) approximately 2 weeks prior to parturition. Colostrum samples were collected from these animals within 24 h postpartum. Serum samples were Rhein-8-O-beta-D-glucopyranoside collected via venipuncture from 12 domestic lambs and.
The virus-neutralizing Ab titer was calculated as the highest dilution yielding less than 50% cytopathic effect
