Mucosal immune response to pathogens in cattle. Antigen presentation is the linchpin of an effective immune response to infectious disease, including Ostertagiosis in cattle, which is caused by parasite O. ostertagi (OO). OO is the most impactful bovine GI nematode parasite in temperate climates, due to chronic infection in the abomasal mucosa. Based on our recent preliminary experiments, we hypothesize that O.ostertagi regulate antigen presentation through modulating immune cells, such as regulatory B cells and antigen presenting neutrophils. We will first define these immune cells in O. ostertagia-infected cattle. Then, we will examine the effects of these immune cells on antigen presentation to T cells from control animals. Finally, we will identify the molecular mechanisms responsible for these regulatory functions, using high throughput proteomics and RNA-Seq.