B Cell and Antibody Responses in Bovine Tuberculosis

Abstract

The development of vaccines and effective diagnostic methods for bovine tuberculosis requires an understanding of the immune response against its causative agent, Mycobacterium bovis. Although this disease is primarily investigated and diagnosed through the assessment of cell-mediated immunity, the role of B cells and antibodies in bovine tuberculosis has been relatively undervalued and understudied. Current evidence indicates that circulating M. bovis-specific antibodies are not effective in controlling the disease. However, local humoral immune responses may contribute to either defence or pathology. Recent studies in animal models and cattle vaccine trials suggest a potential beneficial role of B cells in tuberculosis control. This review discusses the role of B cells and antibodies in bovine tuberculosis and explores antibody-based diagnostics for the disease, including traditional techniques, such as different ELISA, new platforms based on multiple antigens and point-of-care technologies. The high specificity and sensitivity values achieved by numerous antibody-based tests support their use as complementary tests for the diagnosis of bovine tuberculosis, especially for identifying infected animals that may be missed by the official tests.

Keywords: B cells; Mycobacterium bovis; antibodies; bovine tuberculosis; cattle.

Figure 2

Overview of the immune response against bovine tuberculosis [11,12,13,14,15,33,39,40,41,42,47,48,49,50,51].

Figure 1

Relevant aspects of the immune response in tuberculosis. Macrophages (Mo) and dendritic cells (DC) are infected by M. tuberculosis (Mt) or M. bovis (Mb) and subsequently present antigens to T and B cells priming the adaptive immune response. T cells then adopt a Th1 phenotype, characterised by the production of IFN-ɣ, IL-2, and TNF-α. B cells serve as antigen-presenting cells and interact with T cells via specific receptor-ligand molecules and cytokine signalling. Specific B cell subpopulations (CD79a+, CD27+CD38-, CD20+) identified in lung tissue from BCG-vaccinated cattle (Mb), and non-human primates and patients infected with M. tuberculosis (Mt) are associated with the granuloma. B cells differentiate into plasmocytes, which release antibodies targeting Mt. Specific IgA, IgG, IgE, IgD, and IgM antibodies were detected in lung tissues of patients with tuberculosis. The figure highlights the crucial roles of antibodies in tuberculosis, including antibody-dependent cellular cytotoxicity (ADCC+), antibody-dependent activation of natural killer (NK) cells, and antibody-dependent cellular phagocytosis.

Figure 3

Key platforms for antibody detection in tuberculous animals. The specific antigens used in each test are schematically illustrated. Red, white, and yellow droplets represent the types of samples tested in each assay—blood, milk, and urine, respectively.