The effects of continuous and intermittent delivery of antigens of Boophilus microplus on the development of murine antibodies

Abstract

Protective antigens solubilised from the membranes of the midgut (LI-GM) of the adult cattle tick Boophilus microplus were delivered to mice either continuously for up to 4 weeks from osmotic pumps implanted subcutaneously or intermittently in a pulsatile fashion by injections or by a combination of both modes of delivery. The effects of delivery profile on antigen specific antibody levels and avidity were compared. LI-GM delivered either by three injections (weeks 0, 2 and 4), or continuously from osmotic pumps (over 4 weeks) induced similar levels of antibodies in mice. The mode of delivery of LI-GM when in the presence of the adjuvant Quil A did not generally affect either the level or the avidity of the antibody response; indeed a single injection of LI-GM in the presence of Quil A stimulated an immune response similar to that induced by several combinations of pulsatile and of continuous delivery where mice were exposed to antigen and adjuvant for up to 4 weeks. LI-GM incubated at 37°C in vitro and in vivo for periods from 4 h to 14 days was partly degraded into low molecular weight (less than 29 kDa) components. The immunogenicity of LI-GM incubated in vitro for 4 h was significantly decreased, although its antigenicity was not affected after incubation for up to 14 days. In conclusion, delivery of LI-GM continuously from osmotic pumps demonstrated that single-step immunisation of mice with tick antigens was feasible. However, it was also demonstrated that the continuous delivery of antigen was only advantageous (i.e potential for a decrease in the number of times an animal must be handled) compared with delivery by injections when no adjuvant was used. Further work is necessary to establish the effect antigen degradation has in limiting the immune response resulting from continuous delivery of antigen from osmotic pumps.