Comparison of RELMα and RELMβ Single- and Double-Gene-Deficient Mice Reveals that RELMα Expression Dictates Inflammation and Worm Expulsion in Hookworm Infection

Abstract

bResistin-like molecules (RELMs) are highly expressed following helminth infection, where they impact both the host and helminth. While RELM␣ (Retnla) impairs helminth expulsion by inhibiting protective Th2 immunity, RELM␤ (Retnlb) can promote its expulsion. We employed Retnla ؊/؊ and Retnlb ؊/؊ mice to delineate the function of both proteins following infection with Nippostrongylus brasiliensis, a hookworm that infects the lung and intestine. Whereas wild-type (WT) and Retnlb ؊/؊ mice exhibited equivalent infection-induced inflammation, Retnla ؊/؊ mice suffered a heightened inflammatory response, including increased mortality, weight loss, and lung inflammation. In the intestine, Retnla ؊/؊ mice had low parasite egg burdens compared to those of WT mice, while Retnlb ؊/؊ mice exhibited high egg burdens, suggesting that RELM␣ and RELM␤ have functionally distinct effects on immunity and inflammation to N. brasiliensis. To test the importance of both proteins, we generated Retnla ؊/؊ Retnlb ؊/؊ mice. Infected Retnla ؊/؊ Retnlb ؊/؊ mice exhibited similar responses to Retnla ؊/؊ mice, including increased mortality and lung inflammation. This inflammatory response in Retnla ؊/؊ Retnlb ؊/؊ mice negatively impacted N. brasiliensis fitness, as demonstrated by significantly lower worm ATP levels and decreased intestinal worm burden and fecundity. Lung cytokine analysis revealed that Retnla ؊/؊ and Retnla ؊/؊ Retnlb ؊/؊ mice expressed significantly increased levels of interleukin-4 (IL-4). Finally, we generated Retnla ؊/؊ mice on the Rag ؊/؊ background and observed that the effects of RELM␣ were abrogated in the absence of adaptive immunity. Together, these data demonstrate that RELM␣ but not RELM␤ significantly impacts the immune response to N. brasiliensis infection by downregulating the Th2 adaptive immune response in the lung, which protects the host but allows improved parasite fitness. Soil-transmitted helminths (STHs) afflict over 2 billion individuals worldwide and can cause anemia and debilitating symptoms in the lung and intestine (1). Host protection against STHs is dependent on the balance between effector immune responses that promote worm expulsion and immunoregulatory pathways that control excessive infection-induced inflammation (2). Resistin-like molecules (RELMs) are secreted proteins with putative effector and immunoregulatory functions against helminth infections (3, 4). In humans, significant increases in resistin expression occur in both filarial nematode and gastrointestinal nematode infections (5, 6). In mice, RELM␣ and RELM␤, which share sequence homology with human RELM␤, are induced in response to Schistosoma mansoni and the gastrointestinal helminths Trichuris muris, Heligmosomoides polygyrus, and Nippostrongylus brasiliensis (7-11).Despite sharing sequence identity and expression patterns, the putative functions of RELM␣ and RELM␤ in helminth infection are different and involve both host-specific and parasite-specific effects. S. mansoni and N. brasiliensis infection led to increased RELM␣ expr...

Immunity to gastrointestinal nematode infections

“…188 It might also be required for efficient expulsion of N. brasiliensis, although the data are conflicting. 188,189 In contrast, there seems to be no role for RELMb in the expulsion of T. spiralis or T. muris. 187,188 RELMa, on the other hand, is mainly expressed in the pulmonary epithelium and might be important for combating the pulmonary stage of N. brasiliensis.…”

“…187,188 RELMa, on the other hand, is mainly expressed in the pulmonary epithelium and might be important for combating the pulmonary stage of N. brasiliensis. 189 RELMa is further implicated in the function of alternatively activated macrophages, highlighting its role in type 2 immune responses.…”

Macrophages in wound healing: activation and plasticity

“…RELMα activates the enzyme lysyl hydrolase 2 ( Plod2 ), which mediates optimal collagen cross‐linking . Additionally, macrophage‐derived RELMα was implicated in dampening lung inflammation and promoting tissue repair in a model of helminth infection‐induced lung injury with rodent hookworm Nippostrongylus brasiliensis . In this model, gene expression analysis of RELMα‐treated lung macrophages revealed that RELMα promoted expression of genes involved in extracellular matrix remodeling: matrix metalloproteinase 9 ( Mmp9 ), integrin beta 1 ( Itgb1 ) and junctional adhesion molecule A ( F11r ).…”

Hematopoietic cell-derived RELMα regulates hookworm immunity through effects on macrophages

“…11,17,18 Other studies using genetic deletion of RELM or RELM overexpression have suggested instead a beneficial function for RELM in limiting Th2 cytokine-induced inflammation in mouse models of asthma and mouse helminth infection. [19][20][21] Although protective in dampening lung inflammatory responses, RELM paradoxically impaired optimal parasite expulsion in infection with the hookworm Nippostrongylus brasiliensis (Nb). 19,21 The mechanism of RELM -induced immunoregulation has been investigated in in vitro activated bone marrow (BM)-derived macrophages and dendritic cells.…”

“…[19][20][21] Although protective in dampening lung inflammatory responses, RELM paradoxically impaired optimal parasite expulsion in infection with the hookworm Nippostrongylus brasiliensis (Nb). 19,21 The mechanism of RELM -induced immunoregulation has been investigated in in vitro activated bone marrow (BM)-derived macrophages and dendritic cells. 13,[22][23][24] These studies showed that RELM expressed by alternatively activated macrophages (AAMac) dampened CD4 + Th2 cell responses whereas RELM derived from dendritic cells promoted CD4 + IL-10 production.…”