# Characterization of the adaptive cellular and humoral immune responses to persistent colonization of Brucella abortus strain RB51 in a Jersey cow

## TL;DR

This study examines how a Jersey cow's immune system responds to a persistent Brucella abortus vaccine strain in its milk, which can cause human infections.

## Contribution

The study characterizes immune responses in a cow persistently shedding Brucella abortus strain RB51, revealing diminished cellular immunity and elevated humoral immunity.

## Key findings

- Persistent RB51 infection is associated with a lack of peripheral anti-RB51 CD4+ T cell responses.
- High anti-RB51 IgG humoral responses are observed in persistently infected cattle.
- Understanding these immune responses may help improve brucellosis interventions and reduce public health risks.

## Abstract

Brucella abortus strain RB51 is the commercial cattle vaccine used in the United States (US) and many parts of the world against bovine brucellosis. RB51 was licensed for use in 1996, and it has been shown to be safe and efficacious in cattle, eliciting humoral and cellular responses in calves and adult animals. In 2017, an epidemiological trace-back investigation performed by the Centers for Disease Control and Prevention (CDC) identified human cases of brucellosis caused by infection with RB51. These infections resulted from the consumption of unpasteurized dairy products, which were traced back to otherwise healthy animals that were shedding RB51 in their milk. At the current time, six adult Jersey cows have been identified in the U.S. that are shedding RB51 in milk. One of the RB51 shedding cattle was obtained and housed at the National Animal Disease Center (NADC) for further study. Improved understanding of host cellular and humoral immune responses to RB51 in persistently colonized cattle may be achieved by the characterization of responses in shedding animals. We hypothesized, based on the lack of RB51 clearance, that the RB51 shedder animal has a diminished adaptive cellular immune response to RB51. Our data demonstrate that in the presence of persistent RB51 infection, there is a lack of peripheral anti-RB51 CD4+ T cell responses and a concurrently high anti-RB51 IgG humoral response. By understanding the mechanisms that result in RB51 persistence, the development of improved interventions or vaccinations for brucellosis may be facilitated, which would provide public health benefits, including reducing the risks associated with the consumption of non-pasteurized milk products.