MyD88 is necessary for neutrophil recruitment in hypersensitivity pneumonitis

Stephanie C. Nance^*, Ae-Kyung Yi^*^,, Fabio C. Re^* and Elizabeth A. Fitzpatrick^*^,1

^* Departments of Molecular Sciences and
Pediatrics, University of Tennessee Health Science Center, Memphis, Tennessee, USA

¹Correspondence: University of Tennessee Health Science Center, Dept. of Molecular Sciences, 858 Madison Ave., Rm. 601, Memphis, TN 38163, USA. E-mail: efitzpatrick{at}utmem.edu

Hypersensitivity pneumonitis is an interstitial lung diseasethat is characterized by alveolitis, granuloma formation, andin some patients, fibrosis. Using the Saccharopolyspora rectivirgulaanimal model of Farmer’s lung disease, our laboratoryhas demonstrated that neutrophils play a critical role in IFN- ${gamma}$ production during the acute phase of the disease. As IFN- ${gamma}$ isnecessary for granuloma formation, it is important to identifythe factors that lead to neutrophil recruitment during disease.To begin to identify the pattern recognition receptors (PRRs)that initiate chemokine production, leading to neutrophil recruitmentfollowing S. rectivirgula exposure, we examined the role ofMyD88 and TLR2. Our results demonstrate that neutrophil recruitment,as measured by flow cytometry and the myeloperoxidase assay,was abolished in the absence of MyD88 following S. rectivirgulaexposure. The decrease in neutrophil recruitment was likelya result of a significant decrease in production of neutrophilchemokines MIP-2 and keratinocyte-derived chemokine. These resultssuggest that S. rectivirgula interacts with PRRs that are upstreamof the MyD88 pathway to initiate cytokine and chemokine production.In vitro studies suggest that S. rectivirgula can interact withTLR2, and stimulation of adherent cells from TLR2 knockout (KO)mice with S. rectivirgula resulted in a significant decreasein MIP-2 production. However, TLR2 KO mice did not have a reductionin neutrophil recruitment compared with wild-type mice followingS. rectivirgula exposure. The results from our studies suggestthat one or more PRR(s) upstream of MyD88 are necessary forneutrophil recruitment following S. rectivirgula exposure.

Key Words: chemokines • IFN- ${gamma}$ • TLR2