Vaccination protocol and bacterial strain affect the serological response of beef calves against blackleg

The serological response of beef calves was evaluated with different vaccination regimens against blackleg, using an official strain (MT) and a field-collected strain of Clostridium chauvoei as antigens. Sixty calves were randomly allocated to four different groups and were submitted to distinct vaccination protocols with a commercial polyvalent vaccine. Group G1 was first vaccinated at four months of age and a booster shot was given after weaning, at eight months. Group G2 was given the first dose at eight months and a booster shot 30 days later. Group G3 was vaccinated only once at eight months and the control group was not vaccinated. These alternative vaccination regimens were proposed in an effort to adequately protect cattle under open-field farming conditions. Serological evaluations were made by Elisa at 4, 8, 9 and 10 months of age. Both groups receiving booster shots had a significantly increased serological response 30 days later. However, the serum IgG levels against C. chauvoei were significantly higher in the calves that were first vaccinated at four months. At 10 months, the two booster shot groups (G1 and G2) had similar serological responses, while the calves that were treated with a single dose of vaccine at weaning (G3) had a response that was similar to that of the control group. The serological response of the calves was significantly inferior at several of the evaluation times when the field strain of the bacteria was used as a challenge antigen instead of the official MT strain. The serological response of calves that are vaccinated twice was found to be satisfactory, independent of the first injection being made at four or eight months of age. It was also concluded that it would be useful to include local bacterial strains in commercial vaccine production.

B Cell–dependent T Cell Responses

Contact sensitivity (CS) is a classic example of in vivo T cell immunity in which skin sensitization with reactive hapten leads to immunized T cells, which are then recruited locally to mediate antigen-specific inflammation after subsequent skin challenge. We have previously shown that T cell recruitment in CS is triggered by local activation of complement, which generates C5a that triggers C5a receptors most likely on mast cells. Here, we show that B-1 cell–derived antihapten IgM antibodies generated within 1 day (d) of immunization combine with local challenge antigen to activate complement to recruit the T cells. These findings overturn three widely accepted immune response paradigms by showing that (a) specific IgM antibodies are required to initiate CS, which is a classical model of T cell immunity thought exclusively due to T cells, (b) CS priming induces production of specific IgM antibodies within 1 d, although primary antibody responses typically begin by day 4, and (c) B-1 cells produce the 1-d IgM response to CS priming, although these cells generally are thought to be nonresponsive to antigenic stimulation. Coupled with previous evidence, our findings indicate that the elicitation of CS is initiated by rapidly formed IgM antibodies. The IgM and challenge antigen likely form local complexes that activate complement, generating C5a, leading to local vascular activation to recruit the antigen-primed effector T cells that mediate the CS response.

Selective Enhancement of Systemic Th1 Immunity in Immunologically Immature Rats with an Orally Administered Bacterial Extract

ABSTRACT Infant rats primed during the first week of life with soluble antigen displayed adult-equivalent levels of T-helper 2 (Th2)-dependent immunological memory development as revealed by production of secondary immunoglobulin G1 (IgG1) antibody responses to subsequent challenge, but in contrast to adults failed to prime for Th1-dependent IgG2b responses. We demonstrate that this Th2 bias in immune function can be redressed by oral administration to neonates of a bacterial extract (Broncho-Vaxom OM-85) comprising lyophilized fractions of several common respiratory tract bacterial pathogens. Animals given OM-85 displayed a selective upregulation in primary and secondary IgG2b responses, accompanied by increased gamma interferon and decreased interleukin-4 production (both antigen specific and polyclonal), and increased capacity for development of Th1-dependent delayed hypersensitivity to the challenge antigen. We hypothesize that the bacterial extract functions via enhancement of the process of postnatal maturation of Th1 function, which is normally driven by stimuli from the gastrointestinal commensal microflora.