Vaccination of neonatal calves with Mycobacterium bovis BCG induces protection against intranasal challenge with virulent M. bovis

Abstract

Vaccination of neonates with Mycobacterium bovis bacillus Calmette-Guerin (BCG) may be a strategy that overcomes reduced vaccine efficacy associated with exposure to environmental mycobacteria in humans and cattle. Preliminary comparisons indicated that 2-week-old calves produced an immune response to vaccination at least as intense as that observed in adults. Subsequently, five gnotobiotic hysterotomy derived calves aged 1 day were inoculated with BCG and 3 months later were challenged intranasally with virulent M. bovis. The number of tissues with lesions and the pathological extent of these lesions was reduced significantly in vaccinates. Furthermore, lesions were evident in the lung or associated chest lymph nodes of four of five controls but none of five vaccinates. BCG vaccination reduced significantly the level of bacterial colonization. However, lesions in the head associated lymph nodes were observed in three of five BCG-vaccinated cattle. Levels of interferon gamma (IFN-gamma) detected by enzyme-linked immunosorbent assay (ELISA) or enzyme-linked immunospot (ELISPOT) in individual vaccinated animals at challenge did not correlate with subsequent resistance and in general immune responses post-challenge were lower in vaccinated calves. Low IL-10 responses were evident but IL-4 was not detected. Responses to ESAT-6 and/or CFP-10 were evident in four of four control calves that had lesions. Two of the BCG vaccinates with lesions did not produce a response to ESAT-6 and CFP-10, indicating that these antigens did not distinguish vaccinated immune animals from vaccinated animals with lesions. Overall, vaccination of neonatal calves with BCG induced significant protection against disease and has potential as a strategy for the reduction of the incidence of bovine tuberculosis.

Fig. 1

IFN-γ secretion post-BCG vaccination and post-M. bovis challenge. Gnotobiotic calves were vaccinated at 1 day (a) of age with BCG. Control calves (b) were inoculated with medium. Responses were measured for 12 weeks. Subsequently, both BCG-vaccinated calves (c) and control calves (d) were challenged intranasally with M. bovis. Whole blood was stimulated with PPD-A (grey), PPD-B (black) or medium control (white) and IFN-γ secretion in supernatants was assessed by ELISA. Means ± s.d. for groups of five calves are shown.

Fig. 2

Responses of calves to M. bovis specific antigens. Five non-vaccinated calves (a–e) were challenged intranasally with M. bovis. Whole blood IFN-γ responses to ESAT-6 (black bars) and CFP-10 (grey bars) were assessed at the indicated times post-challenge. Results for individual animals are shown: (a) no. 50, (b) no. 54, (c) no. 57, (d) no. 58, (e) no. 59.

Fig. 3

Detection of post-challenge IFN-γ responses by ELISPOT. PBMC from control (a–e) and BCG-vaccinated (f–j) calves were isolated at the indicated time-points post-M. bovis challenge. The number of PPD-A (grey bars)- and PPD-B (black bars)-specific IFN-γ SFC was estimated by ELISPOT. The number of SFC obtained by stimulation with medium control was subtracted from the number of SFC observed following antigen stimulation. Results for individual animals are shown.