Ascaris suum is known to cause ascariasis of both pigs and humans. Ascariasis is associated with a reduced control of intracellular pathogens and decreased vaccine efficacy. All-trans retinoic acid (ATRA), an active metabolite of Vitamin A (VA), is known to mediate a diverse array of physiological and biological processes including immune and inflammatory responses. The phenotype of alveolar macrophages (AM), the most abundant cell in the lung, has not been critically examined during chronic infection with A. suum nor has the effect of administration of dietary ATRA alone or during infection. This combination of treatments is likely common in underdeveloped regions where infection with Ascaris is prevalent and public health initiatives to control nutrient deficiencies often include VA supplementation. In this study we showed that a low dose and repeated "trickle" infection with A. suum alone and with ATRA administration altered the AM cell surface antigen phenotype.