Amblyomma americanum ticks utilizes countervailing pro and anti-inflammatory proteins to evade host defense

Abstract

Feeding and transmission of tick-borne disease (TBD) agents by ticks are facilitated by tick saliva proteins (TSP). Thus, defining functional roles of TSPs in tick evasion is expected to reveal potential targets in tick-Antigen based vaccines to prevent TBD infections. This study describes two types of Amblyomma americanum TSPs: Those that are similar to LPS activate macrophage (M) to express pro-inflammation (PI) markers and another set that suppresses PI marker expression by activated M. We show that similar to LPS, three recombinant (r) A. americanum insulin-like growth factor binding-related proteins (rAamIGFBP-rP1, rAamIGFBP-rP6S, and rAamIGFBP-rP6L), hereafter designated as PIrTSPs, stimulated both PBMC-derived M and mice RAW 267.4 M to express PI co-stimulatory markers, CD40, CD80, and CD86 and cytokines, TNFα, IL-1, and IL-6. In contrast, two A. americanum tick saliva serine protease inhibitors (serpins), AAS27 and AAS41, hereafter designated as anti-inflammatory (AI) rTSPs, on their own did not affect M function or suppress expression of PI markers, but enhanced expression of AI cytokines (IL-10 and TGFβ) in M that were pre-Activated by LPS or PI-rTSPs. Mice paw edema test demonstrated that in vitro validated PI-and AI-rTSPs are functional in vivo since injection of HEK293-expressed PI-rTSPs (individually or as a cocktail) induced edema comparable to carrageenan-induced edema and was characterized by upregulation of CD40, CD80, CD86, TNF-α, IL-1, IL-6, and chemokines: CXCL1, CCL2, CCL3, CCL5, and CCL11, whereas the AI-rTSPs (individually and cocktail) were suppressive. We propose that the tick may utilize countervailing PI and AI TSPs to regulate evasion of host immune defenses whereby TSPs such as rAamIGFBP-rPs activate host immune cells and proteins such as AAS27 and AAS41 suppress the activated immune cells.