Differential expression of vascular endothelial growth factor A (VEGFA) and M1 macrophage marker nitric oxide synthase 2 (NOS2) in lymph node granulomas of BCG-vaccinated and non-vaccinated cattle infected with Mycobacterium

Authors: Kanipe, Carly; Putz, Ellie; Palmer, Mitchell

Submitted to: Tuberculosis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2025
Publication Date: 3/1/2025
Citation: Kanipe, C.R., Putz, E.J., Palmer, M.V. 2025. Differential expression of vascular endothelial growth factor A (VEGFA) and M1 macrophage marker nitric oxide synthase 2 (NOS2) in lymph node granulomas of BCG-vaccinated and non-vaccinated cattle infected with Mycobacterium. Tuberculosis. https://doi.org/10.1016/j.tube.2025.102609.
DOI: https://doi.org/10.1016/j.tube.2025.102609

Interpretive Summary: Cattle can become infected with a bacterium which causes tuberculosis. This bacterium can cause disease in people and can cost cattle farmers a lot of money. There is a vaccine for cattle tuberculosis which can reduce the severity of disease, but it is not consistent and does not prevent infection. A problem with this vaccine is that we do not know how it provides protection. One theory is that it changes the composition of the lesions that form. We examined lesions that formed in both vaccinated and non-vaccinated cattle and compared them to each other. Specifically we looked at markers for inflammation, new blood vessel formation and bacterial burden. We found no differences in bacterial loads between vaccinates and non-vaccinates. The more severe lesions had more inflammatory markers. Vaccination did not affect the levels of blood vessel markers.

Technical Abstract: Mycobacterium bovis (M. bovis) is the causative agent for bovine tuberculosis. The human vaccine, Bacillus Calmette-Guérin (BCG), is an attenuated strain of M. bovis which provides non-sterilizing and highly variable protection against disease in cattle. While lesions have been characterized in non-vaccinated cattle infected with tuberculosis, little has been done comparing them to lesions which form in BCG-vaccinates. In the current study, in situ hybridization was used to examine differences in expression of M. bovis RNA, inducible nitric oxide synthase 2 (NOS2), and vascular endothelial growth factor A (VEGFA) as it relates to vaccination status and granuloma grade, utilizing two different cohorts of cattle. In both groups our data demonstrated no differences (P>0.05) between vaccination groups or granuloma grade in average number of copies of M. bovis mRNA per µm2 of the total granuloma area or per µm2 of the necrotic portion of the granuloma. Within a given vaccination group high grade granulomas had more copies of NOS2 per cell, per µm2 and a higher percentage of cells expressing NOS2 than low grade granulomas. Additionally, granulomas of non-vaccinates had a higher percentage of cells producing NOS2 than vaccinates. Both findings were true for both cohorts. More specific nuances between granuloma grade and vaccination status varied between experimental groups. In one cohort non-vaccinated animals produced more NOS2 than vaccinates for both high- and low-grade granulomas, however the second cohort had lower NOS2 in high-grade granulomas of non-vaccinates but higher NOS2 in low grade granulomas. Vaccination status and granuloma grade did not affect the average copies of VEGFA per cell or the percent of cells expressing RNA in either experimental group. In Group 2, BCG vaccinates had higher average of copies per µm2 than non-vaccinates, but this was not true in Group 1. Collectively these findings demonstrate that NOS2 and VEGFA are likely not mechanisms of BCG vaccination protection however they may play a role in disease severity.