Tick Bites in Transmission of the Alpha Gal Allergen Eliciting Red Meat Allergy

Tick bites are thought to be the cause of red meat allergy, diagnosed by occurrence of hives, shortness of breath and anaphylaxis 3-5 hours after eating red meat, such as pork, beef, and lamb. A growing number of cases of red meat allergy have been reported in the southern and eastern U.S. (up to 3,500 cases in North Carolina alone), but it is also prevalent elsewhere, including Europe, Asia, and South America. Studies have demonstrated links between the occurrence of specific tick species (including lone star tick, Amblyomma americanum) in geographical regions in occurrence of red meat allergy in the U.S.

Red meat allergy is caused by an unusually high allergic response against galactose-alpha-1,3-galactose (aGal), which is a common glycan in nearly all mammalian tissue, with the exceptions of Old World monkeys and humans. The source of the allergen aGal delivered through tick bites is still enigmatic because ticks do not produce aGal. In addition, it is unclear why red meat allergy results in only a relatively small subset of the cases among frequent tick bites of humans.

We hypothesize that ticks mediate the 'transmission' of the aGal allergen by injection of tick saliva containing aGal glycans acquired from a prior intrastadial (same molting stage) blood meal on non-human mammals. This hypothesis is further expanded to implicate males of certain species of ticks (i.e., lone star tick in the U.S.) as having particularly high opportunities for transmitting the allergen to humans. Our preliminary study supports this hypothesis: the salivary glands of male lone star tick contains extremely high levels of aGal allergen. Because male ticks engage in multiple intrastadial feedings in the adult stage, they have significant opportunity to switch feeding hosts from non-human mammals to humans within the same life stage. The objective of this study is to identify the allergenic ticks (species, stage, gender, and prior host in the feeding) and to characterize the allergenic salivary components by using a novel mutant mouse model - an alpha-galactosyltransferase knockout mutant mouse (aGT-KO).

The specific aims are:

(1) Test whether the bites of the ticks previously fed intrastadially on non-human mammals cause red meat allergy, using a mutant mouse aGT-KO as a humanized model system for aGal response.

(2) Isolate, identify, and characterize the tick salivary proteins containing aGal glycosylation.

(3) Survey of field-collected ticks to identify the species, stage, gender, and the host of the ticks carrying aGal immunogens.

This proposal addresses these Focus Areas (Fiscal Year 2017 Tick-Borne Disease Research Program) by:

• 'Pathogenesis/ New research tools to support studies of pathogenesis': By using a new model for RMA study aGT-KO mouse in Specific Aim 1.

• 'Pathogenesis/ Host-Pathogen interactions': By identifying the immunogen in Specific Aim 2.

• 'Prevention/ Interrupting the cycle of the disease agents in nature': By surveying field-collected ticks for the aGal.

This proposal is innovative in several aspects. First, the experimental system developed in this study, using aGT-KO mutant mouse, will establish a new tool for surveying the roles of other tick species from different ecological and feeding backgrounds in red meat allergy; e.g., ticks pre-fed on different host animals. We will study the roles of male A. americanum, which has been overlooked as an agent in direct damage and pathogen transmission because of its short feeding duration. The ultimate goal of this work is to establish methods for minimizing or eliminating the risk of RMA by elucidating the source of the RMA allergen and mechanism for its transmission. In addition, the knowledge obtained in this study provides foundational work for a novel concept: the use of host proteins and glycans in tick saliva to effectively evade the host's immune system.