Molecular characterization and related aspects of the innate immune response in ticks.

Compared to insects, little is known about innate immunity in ticks. This chapter addresses the molecular processes that recognize non-self and the cellular and molecular processes mobilized to phagocytose, engulf, inhibit or kill invaders. We discuss the receptors that recognize pathogen associated molecular patterns (PAMPs) and the putative up-regulation of regulatory cascades that lead, ultimately, to cellular or molecular responses. We describe the molecular events that activate the cellular processes and the array of humoral factors that are mobilized against invading organisms, including antimicrobial peptides, proteases and protease inhibitors, lectins, coagulation factors and others. Special attention is directed to the antimicrobial activity of the midgut, the initial site of contact for microbes ingested with the blood. Blood feeding and digestion alone up-regulates an impressive array of proteins, e.g. oxidative stress reducing proteins, lectins, protease inhibitors, proteases, hydrolases, protein/lipid binding agents. Finally, we compare the innate immune responses of ticks with insects and other invertebrates and note deficiencies in our knowledge tick innate immunity.