Produção de óxido nítrico e interferon – gama por células mononucleares do sangue periférico de bovinos infestados por Boophilus microplus

Abstract

Tick infestations in cattle reduce its beef and dairy productivity causing great economic losses to livestock. The potential damages are physical weakness, transmission of diseases to the herd, as anaplasmosis and babesiosis, and even vulnerable animals deaths. Thus, the tick control has been considered priority in tropical regions worldwide. The ticks remain fixed to their hosts for long periods being exposed to the cattle defense system; it causes inflammation and activates the host’s humoral and cellular immune response. Nevertheless, immunogenic components of the salivary gland of cattle tick modulate the response to profiles of cytokines that promote the blood-feeding. There are few studies approaching immune mechanisms that lead to host-parasite interaction and determine the success or unsuccessful of parasitism. Recent works suggest the importance of genetic factors related to the resistance to ticks in Bos taurus and Bos indicus breeds. In addition, studies show the critical role of cytokines in the prevention and progression of diseases. The aimed of this work was to evaluate the immune response in cattle artificially infested by Boophilus microplus through cell proliferation assays and detection of nitric oxide (NO) and interferon-gamma (IFN-) in peripheral blood mononuclear cells, in order to establish different resistance levels in Girolando breed. Six tick-resistant and six tick-susceptible animals from a F2 population of 332 animals originated from crossing cattle F1 (½ Holstein : ½ Gir) were selected based on the ticks counting and breeding value. Blood samples were collected for cell culture and stimulation in vitro with antigens of B. microplus in the points 0, 5 and 12 days after infestation. The cell proliferation and the NO and IFN- levels were evaluated by MTT, Griess and ELISA, respectively. There was a tendency of increasing proliferation of resistant animals (R) cells in the 5th day when they were stimulated with the tick antigens, returning to initial levels at 12th day. In the other hand, for the susceptible animals (S) the stimulation seemed to inhibit proliferation of cells in day 0, and did not altered the rates of 5th and 12th day. There was no significant difference between the cell proliferation of the groups R and S. When the cells obtained in the day 0 were cultured in the absence of stimulation, the levels of NO of animals R tended to be higher than that of the animals S. The stimulation with tick antigens inhibited the NO production by cells of animals R in the 5th day. In addition, there was no significant difference in NO and IFN- production between the groups R and S. The results suggest that NO may play a role in the early immune response that outlines the mechanism of resistance to ticks, since the most important changes were detected until the 5th day after the infestation. It is possible that the resistance mechanism is associated to the downregulation of immune response in order not to encourage the modulation by the ticks, although being effective enough to eliminate it. An evaluation of the immune response in the first moments after the tick fixation to cattle leather, as well as a more detailed monitoring of the temporal points of the infestation, could provide more conclusive data.