Twenty calves were orally infected with Mycobacterium paratuberculosis before weaning. Ten of these plus 4 non-infected controls were maintained on elevated dietary iron intake from 6 to 33 months of age. During this time, in which the majority of animals were bred, the influence of increased dietary iron upon tests of cellular and humoral immune responsiveness to antigens of the organism were monitored. Results were examined in relation to the organism's capacity to multiply and infect up to 7 portions of the intestinal tract. No significant differences were detected in the degree of intestinal disease or pattern of faecal excretion of M. paratuberculosis in iron supplemented and non-supplemented cattle. Cutaneous delayed-type hypersensitivity (DTH) to johnin PPD developed at 1 month and in-vitro lymphocyte and immunostimulatory activity (LS) to this antigen at 2 months after infection. LS indices were significantly reduced in magnitude in iron-supplemented cattle (p less than 0.01). Most ELISA antibody responses were positive 10 to 17 months after infection and preceded the fewer number of CF responses by several months. Neither of the antibody tests was affected by elevated iron intake. Generally, complete or partial resistance to paratuberculosis was associated with sustained positive monthly LS tests (index greater than or equal to 2.0), whereas antibody levels tended to be sustained only in the more severely affected cattle. Although neither test system was affected by pregnancy the ELISA failed to detect a significant proportion of cattle chronically shedding M. paratuberculosis in faeces.
The degree of piliation of 29 haemolytic and 4 non-haemolytic Australian strains of Moraxella bovis representing 7 different pilus antigen groups was determined. The infectivity and virulence for the eye was measured in steroid-treated mice and in cattle. Non-piliated strains failed to infect the murine eye. Most moderately or heavily piliated strains reproducibly produced the highest infectivity and virulence scores in mice when compared with lightly or very lightly piliated strains (p less than 0.05). Non-haemolytic, piliated strains were infective and in one instance virulent for mice. Almost similar levels of infectivity and virulence were observed for 7 representative haemolytic strains tested in both cattle and mice. The relative molecular weight of pilin sub-units was compared using sodium dodecyl-sulphate polyacrylamide gel electrophoresis. Three classes of pili, alpha, beta and gamma of ascending sub-unit size were identified among the 7 pilus antigen serogroups. Pilin sub-unit size bore no relationship to the degree of piliation but most strains that were highly virulent in mice and cattle expressed alpha and gamma sub-units. Some strains appeared capable of switching from alpha to beta or form beta to gamma sub-unit production.
Complete desensitization to tuberculin skin-testing (anergy) was produced in cattle by repeated intravenous injections of living BCG organisms into animals sensitized by a prior subcutaneous dose of BCG. Two levels of desensitization were produced; complete desensitization following 10 i. v. doses and partial desensitization following 5 i. v. doses of 100 mg BCG. Intradermal tuberculin testing at the end of the experiment stimulated the appearance of reactive blood lymphocytes in sensitized cattle as measured by in vitro 3H-thymidine uptake. The cattle which were partially desensitized showed this response but the completely desensitized cattle did not. Reactivity of blood lymphocytes in vitro to PHA and Brucella abortus antigen was not depressed in the anergic cattle. Serum antibody titres to BCG polysaccharide, PPD, or whole BCG organisms showed remarkably little change during the i. v. desensitizing injections of BCG. Differential blood leucocyte counts also remained within normal limits during this period. The production of MIF by blood lymphocytes from the anergic cattle appeared to be unimpaired. Using 3H-thymidine uptake by lymphocytes from sensitized cattle, it was found that serum from desensitized cattle did not inhibit lymphocyte stimulation with tuberculin. It was concluded that the lack of tuberculin-sensitized lymphocytes in the blood of anergic cattle may have been due to their removal from the recirculating pool and their continued suppression in lymphoid tissue.
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