Characterization of IL-10-producing neutrophils in cattle infected with Ostertagia ostertagi

Authors: LI, LEI - University Of Maryland; SI, HONGBIN - University Of Maryland; WU, SHU-WEI - University Of Maryland; MENDEZ, JONATAN - University Of Maryland; Zarlenga, Dante; Tuo, Wenbin; XIAO, ZHENGGUO - University Of Maryland

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2019
Publication Date: 12/30/2019
Citation: Li, L., Si, H., Wu, S., Mendez, J.O., Zarlenga, D.S., Tuo, W., Xiao, Z. 2019. Characterization of IL-10 producing neutrophils in cattle infected with Ostertagia ostertagi. Scientific Reports. 9:20292. https://doi.org/10.1038/s41598-019-56824-x.
DOI: https://doi.org/10.1038/s41598-019-56824-x

Interpretive Summary: An immune modulator, interleukin-10 (IL-10), is known to be essential to regulate and maintain bovine immunity. However, the source of IL-10 during immune responses is unclear. Our previous work demonstrates that Ostertagia ostertagi, a bovine stomach nematode worm, induces massive B cell expansion in lymph nodes draining the stomach, but even such as drastic host response is unable to resolve the infection. Our present study found that most of the bovine neutrophils produced IL-10 and some of which had moderate levels of cell surface major histocompatibility complex class II antigen, a group of membrane proteins key to initiation of immune responses. Treatment of neutrophils with Ostertagia worm extract increased production of IL-10. Further, co-culture of neutrophils with T cells enhanced T cell activation. IL-10 depletion increased T cell activation; however, Ostertagia worm extract suppressed T cell activation. The function of neutrophils to activate T cells was contact-dependent. Interestingly, dead neutrophils also inhibited T cells. The results from our study indicate that neutrophils may play a critical role in regulating the activation of bovine T cells and the nematode parasite O. ostertagi may evade the host immunity by inducing IL-10 production by neutrophils, a most abundant subset of immune cells and the first line defender of the bovine host. This research will benefit the cattle industry, veterinarians and researchers in the immunology and vaccine development fields.

Technical Abstract: IL-10 is known to play a critical role in the regulation of T cell activation in cattle. However, it is unclear about the source of IL-10. Upon infection with Ostertagia ostertagi (OO), the bovine immune system initiates massive B cell expansion/infiltration in the abomasal draining lymph nodes, but fails to resolve the infection. We found that the majority of bovine neutrophils in circulation and in secondary lymphoid tissues produced IL-10 in both grass-fed and grain-fed cattle. Exposure to OO extract in vitro increased neutrophil production of IL-10 in a dose-dependent manner. Interestingly, MHC II was also expressed at a moderate level in approximately 10 to 20% of the neutrophils from the blood and spleen, suggesting a potential antigen-presentation role for neutrophils. Indeed, co-culture of neutrophils with anti-CD3 Ab-stimulated CD4+ T cells led to enhanced T cell activation as demonstrated by increased proliferation and expression of CD25. While IL-10 depletion by neutralizing Ab enhanced CD4+ T cell activation with and without OO extract, the presence of OO extract decreased the expression of CD25 on CD4+ T cells. This may indicate that OO extract influences the T cell-stimulatory function of neutrophils in addition to enhancing IL-10 production. Furthermore, this function of neutrophils was shown to be contact-dependent, as separation of neutrophils from CD4+ T cells using transwell completely abolished their T cell stimulatory functions. Of interest, even dead (paraformaldehyde-fixed) neutrophils had an inhibitory effect on T cells, suggesting neutrophils may engage in comprehensive regulation of activated T cells in cattle. Neutrophils could be an important player in regulating the activation of CD4+ T cells in cattle, and IL-10 production could be co-opted by pathogens to tune down the host's immune response and facilitate pathogen survival.