Abstract
The mechanisms underlying tick resistance within and between cattle breeds have been studied for decades. Several previous papers on bovine immune parameters contributing to tick resistance discussed findings across DNA, RNA, protein, cellular, and tissue levels. However, the differences between bovine host species, tick species and the experimental layouts were not always taken into account. This review aims to (a) give a comprehensive summary of studies investigating immune marker differences between cattle breeds with varying degrees of tick resistance, and (b) to integrate key findings and suggest hypotheses on likely immune-regulated pathways driving resistance. Experimental issues, which may have skewed conclusions, are highlighted. In future, improved experimental strategies will enable more focused studies to identify and integrate immune markers and/or pathways. Most conclusive thus far is the involvement of histamine, granulocytes and their associated pathways in the tick-resistance mechanism. Interestingly, different immune markers might be involved in the mechanisms within a single host breed in contrast to between breeds. Also, differences are evident at each tick life stage, limiting the level to which datasets can be compared. Future studies to further elucidate immune molecule dynamics across the entire tick life cycle and in-depth investigation of promising markers and pathways on both molecular and cellular level are in dire need to obtain a scientifically sound hypothesis on the drivers of tick resistance.
Highlights
The economic importance of ticks and the need to control them was realized alongside the discovery of their potential as vectors of harmful parasites, to livestock (Hunter and Hooker, 1907; Theiler, 1911)
We propose a role for IgE-dependent responses as one of the drivers of resistance, and as such, daily data on the IgE levels throughout the period of tick attachment and subsequent life stages will be of great importance
Few immune markers have been investigated with sufficient depth to obtain a picture of events involved in the cattle tick-resistance mechanism
Summary
The economic importance of ticks and the need to control them was realized alongside the discovery of their potential as vectors of harmful parasites, to livestock (Hunter and Hooker, 1907; Theiler, 1911). Taurus breeds (Riek, 1962; Wagland, 1978, 1980; Rechav et al, 1990). The majority of studies indicate that resistance is acquired through exposure to ticks (Wagland, 1975, 1980; George et al, 1985; Momin et al, 1991) and that resistance is acquired sooner and to a higher degree in B. t. This phenotype only becomes apparent after subsequent (and not initial) tick exposure in B. t. Indicus and mixed breed cattle (Roberts, 1968a; Wagland, 1975; Hewetson and Lewis, 1976) This phenotype only becomes apparent after subsequent (and not initial) tick exposure in B. t. taurus, B. t. indicus and mixed breed cattle (Roberts, 1968a; Wagland, 1975; Hewetson and Lewis, 1976)
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