Immunity Induced by Vaccination with Rhipicephalus appendiculatus Salivary Gland Antigens Does Not Augment Protective Immunity Acquired Naturally by Exposing Rabbits to Adult Ticks

Abstract

A study was conducted using rabbits to ascertain the effects of immunity induced with salivary gland antigens (SGA) on naturally acquired host resistance, which was confirmed by exposing groups of rabbits to adult Rhipicephalus appendiculatus (Neumann) ticks. A reciprocal experiment was conducted to establish the effect of naturally acquired resistance on vaccination with SGA. After the acquisition of resistance by either method of vaccination, rabbits were then challenged with the 3 life stages of the tick. Results of the experiment demonstrated 3 phenomena: infestation of rabbits with 60 adult ticks leads to high protection in terms of reduction in the engorged weight against adult ticks, larvae, and nymphs (88.6, 31.5, and 55.9%, respectively); vaccination alone provides 53.9, 29.7, and 35.7% reduction in adult, larval, and nymphal ticks, respectively; and vaccination of rabbits already exposed to adult tick infestation appeared to have no additive immunological benefit above that already provided by adult ticks. Sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analyses revealed that antibodies with high avidity to SGA were directed to a 39-kDa polypeptide. This polypeptide was not revealed by sera from rabbits that were first infested with adult ticks. Sera from rabbits that were first vaccinated with SGA consistently reacted with the 39-kDa polypeptide. Sera from rabbits that were infested recognized strongly a 42-kDa polypeptide among 5 polypeptides in the SGA. Results of the experiment show that resistance resulting from adult tick infestation is not augmented by immunity caused by vaccination with SGA.