Imunobiologia das infestações de bovinos pelo carrapato Rhipicephalus (Boophilus) microplus: estudo dos correlatos imunes de resistência e de susceptibilidade / The immunobiology of infestations with the cattle tick Rhipiceplahus (Boophilus) microplus: comparative immunologic and molecular studies of the tick-host interface in susceptible and resistant bovine hosts.

Alessandra Mara Franzin

The skin of vertebrates is the largest for over 15,000 species of hematophagous arthropods. Among them are ticks, which are long-term feeders and interact with host defenses for days to weeks. Little is known about specialized strategies for eliminating ectoparasites, but ticks can induce immune responses in host. Bovines present variable and heritable levels of resistance to the Ripicephalus (Boophilus) microplus and are the only model in which distinct outcomes of infestation can be examined in the same species of host. In order to obtain some of the immune correlates of these outcomes, we quantified populations of leukocytes and lymphocytes present in the inflammatory infiltrates elicited by tick bites in skin of resistant and susceptible bovine breeds, respectively, Bos taurus indicus and Bos Taurus taurus. As expected, ticks induce cutaneous inflammatory infiltrates around their mouthparts. However the composition of infiltrate presented with significant differences that varied according to the phenotype of infestation. Inflammation of resistant breed contained significantly more basophils than in susceptible adult-infested skin (P<0.05). Eosinophils were absent in skin from naïve animals, but were present in normal and infested skin. They were present in infested skin of both breeds and more significantly so in nymph and adult-infested skin of resistant breed (P<0.05). However, mast cell numbers were equally diminished in nymph and adult-infested skin of both breeds when compared with non-infested skin (P<0.05). The neutrophils were equally present in infested skin of both breeds, but they are more numerous in skin infested with adults than with nymphs (P<0.05). Conversely, mononuclear cells were more abundant in skin infested with nymphs than with adults (P=0.001). Bites by nymphs and adults recruit more CD3+ T cells in skin of resistant breeds than in that of susceptible ones (P<0.05). The CD4+ populations of cells 11 were more numerous in adult-infested skin of resistant than in that of susceptible (P<0.05); CD8+ cells were increased in nymph-infested skin of resistants relative to that of susceptibles (P<0.05). The population of gd/WC1+ T cells were more abundant (P<0.05) in adult-infested skin of resistant when compared with those found in control skin of the same animals. The numbers of B lymphocytes were diminished in nymph and adult-infested skin of susceptibles when compared with those found in control skin (P<0.05); in adult-infested skin of resistants, B lymphocytes were more numerous (P <0,05) than in skin of susceptibles. Bites by nymph and adult tends to recruited more Natural Killers cells to skin in resistant breed than in susceptible one (P >0,05). The results suggest that mast cells are source of cytokines and inflammatory mediators that play effectors and modulator roles in immune responses, their reduction possibly due to degranulation by tick saliva. Amount of neutrophils in infested skin may reflect the fact that only nymphs express RGD-containing disintegrins, which are possibly neutrophils-specific. Eosinophils, as well as basophils, are important to ticks resistance, their skin kinetic suggesting a systemic effect of tick infestations. Basophils resistant host increasing suggesting that they are the pivotal cells that impair haematophagy. The observed increase of CD3+ T cells in nymph and adult-infested skin of resistants suggests their importance to regulate anti-tick immune responses. The diminished numbers of B cells in susceptible breed indicate that antibodies are important in acquired resistance to ticks. On the other hand, the reduction of gd/WC1+ T cells seen in the infested skin of susceptible bovines indicates that these cells may play a role in resistance to ticks. Natural Killers cells could help the development of efficacious immune responses to ticks-borne diseases. In conclusion, these results reflect the fact that local responses involve resident and infiltrating leukocytes and lymphocytes that are sources of immunoregulatory, effectors and memory responses elicited against ticks.

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