Tick saliva is a complex mixture serving a variety of functions. Soon after attachment, ixodid ticks (except a few species of Ixodes) secrete a milky white material that hardens into a latex-like cone surrounding the hypostome. This is the initial core of the cement cone.
Additional secretions over the next 48-72 hours add cortical layers to the cement; in some species this added cement secretion flows over the skin of the host to further strengthen the attached parasite.
The chemical composition of the cement consists of a mixture of antigenic and non-antigenic proteins, with substantial lipid and carbohydrate in the innermost layers, the latter compounds mostly in the form of lipo- and glycoproteins. Following establishment of the cement cone, the salivary glands of the feeding tick expand and protein synthesis accelerates.
New proteins were found to have been generated by the glands following the attachment stimulus, while other proteins also present in the unfed glands increased in quantity.
The feeding period is accompanied by copious secretion of salivary fluids. This pattern of salivary gland activity parallels the sequence of attachment, wound site formation, feeding, mating and repletion that characterises the parasitic period.
In addition to the cement precursors described previously, histochemical tests have demonstrated a variety of enzymes in the secretory cells of the salivary glands.
Whether some or all of these enzymes are secreted and contribute to the formation of the feeding site or fluid uptake is unknown. Certain salivary enzymes are capable of cleaving complement, leading to the production of amaphylatoxins.
Tick salivary glands secrete also a veritable cornucopia of pharmacologically active substances, including anticoagulants, prostaglandin E2 (PGE2) and prostacyclin, vasodilators, apyrase, antiinflammatory agents, anti-histamines (in some species) and others. In some species, enzymes are secreted that destroy bradykinins and anaphylatoxins, host proteins that play crucial roles in modulating the inflammatory response. In certain very successful host/parasite associations, e.g., the deer tick Ixodes scapularis (dammini), and the white footed mouse Peromyscus leucopus, unknown salivary agents suppress components of the host immune system, e.g., T.-cells, thereby minimising rejection.
- Sonenshine DE: Biology of Ticks. Part 1, 1991, Oxford UniversityPress, New York