Antibody Levels to Recombinant Tick Calreticulin Increase in Humans after Exposure to Ixodes scapularis (Say) and Are Correlated with Tick Engorgement Indices

Abstract

The antibody responses of subjects who presented with a definite Ixodes scapularis (Say) tick bite were measured to determine the utility of the antibody response against recombinant tick calreticulin (rTC) as a biologic marker of tick exposure. Subjects bitten by I. scapularis evidenced an increase in anti-rTC antibody levels between visit 1 and visit 2 from 24.3 to 27.1 ng/microl serum (n = 88, p = 0.003), and levels remained elevated at visit 3 (p = 0.005). These anti-rTC antibody levels during visits 2 and 3 were significantly higher than those in four non-exposed controls. Tick engorgement indices, measured on the biting ticks, were found to be correlated with anti-rTC antibody levels (e.g., for visit 3: Pearson's r = 0.357, p = 0.001). Tick engorgement index (TEI), ratio of body length to scutal width, was identified to be the only independent predictor of anti-rTC antibody levels in linear regression models. Logistic regression revealed that a bite from an I. scapularis tick that became engorged (TEI >3.4) was a risk factor for anti-rTC antibody seropositivity (adjusted odds ratio for age and bite location = 7.4 (95% confidence interval 2.1-26.4)). The anti-rTC antibody test had a sensitivity of 0.50 and a specificity of 0.86 for a bite from I. scapularis that became engorged. Immunoblotting revealed that subjects made a specific anti-rTC antibody response.

Human immune response to sand fly salivary gland antigens: a useful epidemiological marker?

“…20 Use of a recombinant salivary protein from the tick Ixodes scapularis is now being used as a marker of exposure to the vector of Lyme disease, where antibody responses to the recombinant salivary calreticulin homologue correlate with the degree of engorgement of the tick on human. 26,27 Serum IgG responses against Phlebotomus papatasi did not differ among the 4 groups tested (Figure 2). Although this result supports the conclusion that the response to L. longipalpis antigens is not an artifact due to nonspecific polyclonal IgG activation, it does not exclude the possibility of cross reactivity between antigens of L. longipalpis and P. papatasi, or, for that matter, any other arthropod antigen.…”

Ixodes scapularistick saliva proteins sequentially secreted every 24h during blood feeding

“…Additionally one protein was identified in I. scapularis nymphs as an immunogenic protein that bound to human serum from exposure to tick bites [198]. The remaining proteins were found in saliva proteomes of R. microplus (n = 28, [50]), H. longicornis (n = 22, [52]), D. andersoni (n = 2, [51]), O. moubata (n = 5, [53], sequencing of I. scapularis tick saliva by Edman degradation (n = 4) [48], and others were verified as secreted in western blotting studies [42,43,[199][200][201][202][203][204].…”

Anti-arthropod saliva antibodies among residents of a community at high risk for Lyme disease in California.

“…6,[55][56][57] For example, the antibody responses of rabbits against the saliva of Amblyomma americanum and D. variabilis ticks were found to possess unique and shared components. 55 Antibodies directed against low molecular mass (Ͻ 20 kD) salivary gland antigens present in Amblyomma americanum may be specific for this tick, whereas antibodies against high molecular mass (85, 86.3, and 111 kD) salivary gland antigens in D. variabilis may be specific for the latter.…”

“…Moreover, the antibody responses of humans against recombinant tick calreticulin (rTC), a cDNA-derived protein isolated from the salivary glands of Amblyomma americanum, can be used as a biologic marker of previous tick exposure. 56,57 Because tick calreticulin cannot be detected in the saliva of feeding ticks until the third day of attachment, it may be particularly useful as a marker for tick bites of longer duration. Also, a cDNA-derived protein is more convenient to use than whole salivary glands as antigen in an assay, and it may confer improved specificity because the antibody measured is directed against an individual protein.…”