Hookworm-Induced Persistent Changes to the Immunological Environment of the Lung

Abstract

A number of important helminth parasites of humans have incorporated short-term residence in the lungs as an obligate phase of their life cycles. The significance of this transient pulmonary exposure to the infection and immunity is not clear. Employing a rodent model of infection with hookworm (Nippostrongylus brasiliensis), we characterized the long-term changes in the immunological status of the lungs induced by parasite infection. At 36 days after infection, alterations included a sustained increase in the transcription of both Th2 and Th1 cytokines as well as a significant increase in the number and frequency of alveolar macrophages displaying an alternatively activated phenotype. While N. brasiliensis did not induce alternate activation of lung macrophages in STAT6؊/؊ animals, the parasite did induce a robust Th17 response in the pulmonary environment, suggesting that STAT6 signaling plays a role in modulating Th17 immunity and pathology in the lungs. In the context of the cellular and molecular changes induced by N. brasiliensis infection, there was a significant reduction in overall airway responsiveness and lung inflammation in response to allergen. In addition, the N. brasiliensis-altered pulmonary environment showed dramatic alterations in the nature and number of genes that were up-and downregulated in the lung in response to allergen challenge. The results demonstrate that even a transient exposure to a helminth parasite can effect significant and protracted changes in the immunological environment of the lung and that these complex molecular and cellular changes are likely to play a role in modulating a subsequent allergen-induced inflammatory response.Historically, an infection with one or multiple helminth parasites has been essentially universal for human populations. It is estimated that a majority of living humans have a history of or are currently infected with a helminth parasite, with the highest prevalence of exposure in developing areas (11). A number of important helminth parasites such as hookworm, Ascaris, and Schistosoma have incorporated a short-term residence in the lungs as an obligate phase of their life cycle. The significance of the lung phase to the developmental biology of these parasites has not been clearly defined. Equally unclear is the impact that the pulmonary phase has on the immunobiology and pathogenesis of infection and the nature and extent to which the immunological environment of the lung is altered by these transient exposures. If significant changes to the pulmonary environment do ensue, to what extent do they influence the level and nature of the responses to subsequent challenges from bacteria, fungi, viruses, and allergens?In recent decades, the incidence and prevalence of allergy and asthma have increased dramatically in industrialized nations, with no comparable increase in developing regions of the world (3, 9, 10, 39). Although a number of factors have been proposed to explain this difference in disease prevalence in developed and developing regions, incl...

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

“…On the other hand, it is also possible that the active concentrations of both RELM proteins may be different, which could impact the biological significance of the different concentrations of these proteins in different tissues. Even though N. brasiliensis is expelled between day 9 and day 12 postinfection in WT mice, previous studies have shown long-lasting inflammatory changes in infected tissue even following worm clearance (21)(22)(23). At day 30 postinfection, we observed increased RELM␣ levels in serum and all infected tissues, while the RELM␤ level was significantly increased in serum, suggesting that N. brasiliensis infection induces persistent changes in RELM␣ and RELM␤ expression levels that may be functionally significant.…”

Dynamics of lung macrophage activation in response to helminth infection

“…Infection with Nb results in a number of immediate and longterm changes to the immunological status of the lungs, including quantitative and phenotypic changes in the macrophage population [10,13,17,42]. In the current study, we describe two distinct morphological forms that develop within the lung macrophage population after a hookworm infection-a vacuolated, foamy phenotype that was supplanted within a few days PI by a persistent population of enlarged macrophages that contained dense granules in the cytoplasm (Fig.…”

“…It is not clear if the origin of these cells is connected. Although it is possible that foamy macrophages transform into the cells with the granular morphology, it is equally likely that these distinct cell types represent at least two different populations whose phenotypes are influenced by the dynamics of the cellular and cytokine changes that persist in the PI lung environment [42].…”

“…Expression profiles of day 2 PI cells isolated from whole lung showed induction of the genes encoding ARG1, FIZZ1, YM1, and AMCase and the lectin MSR1, all hallmark indicators of alternative activation [5]. AAMs are induced by a combination of the rapid induction of Th2 cytokines [13] and tissue injury [51] caused by the Nb larvae as they enter the lungs and then sustained by the long-term changes to the immunological environment of the lung [42].…”

ILC2s and T cells cooperate to ensure maintenance of M2 macrophages for lung immunity against hookworms

“…An important associated feature of Nb infection is the significant damage to the epithelium and vasculature of the lung resulting from worm penetration and subsequent migration through the parenchyma into the airways 2,9 . In a primary infection, the host immune response to these events appears too slow to affect worm survival or fecundity.…”