Identification of Anaplasma marginale adhesins for bovine erythrocytes using phage display

Authors: Noh, Susan; UJCZO, JESSICA - Former ARS Employee; ALPERIN, DEBRA - Washington State University

Submitted to: Frontiers in Tropical Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2024
Publication Date: 6/25/2024
Citation: Noh, S.M., Ujczo, J.K., Alperin, D.C. 2024. Identification of Anaplasma marginale adhesins for bovine erythrocytes using phage display. Frontiers in Tropical Diseases. 5. https://doi.org/10.3389/fitd.2024.1422860.
DOI: https://doi.org/10.3389/fitd.2024.1422860

Interpretive Summary: Bovine anaplasmosis, caused by Anaplasma marginale, has a worldwide distribution and is one of the most common tick-borne diseases of cattle. Anaplasma marginale primarily infects red blood cells leading to anemia, decreased weight gain, decreased milk production, and unexpected outbreaks resulting in high mortality. Methods to prevent bovine anaplasmosis are currently limited, though protection from disease can be reliably achieved through immunization. However, selection of antigens for testing and inclusion in a vaccine is a major limitation in the development of a low cost vaccine. Because A. marginale is an obligate intracellular pathogen, surface proteins that mediate adhesion and entry into host cells are high priority vaccine candidates. Thus, goal of this work was to identify a broad array of A. marginale surface proteins that may mediate adhesion to bovine erythrocytes. To do this, we expressed 66 A. marginale proteins on the surface of small viruses, known as phage. We mixed the phages with RBCs from cattle. We then recovered the phages that bound bovine erythrocytes and identified the A. marginale proteins. Overall, 73% of A. marginale proteins were eliminated due to poor binding to RBCs. Importantly, eleven proteins that bound bovine RBCs were identified. Many of these proteins will serve as high priority vaccine candidates.

Technical Abstract: Bovine anaplasmosis, caused by Anaplasma marginale, is one of the most common tick-borne diseases of cattle and has a worldwide distribution. The high costs of bovine anaplasmosis are due to treatment, decreased production, and outbreaks resulting in high mortality. The impact of bovine anaplasmosis is greatest in tropical and subtropical regions where tick vectors are abundant year around. Prevention generally relies on the use of tetracyclines to prevent disease and acaricides to reduce tick burdens. Thus, additional methods to prevent disease while reducing the use of antibiotics are needed. Protection can be reliably achieved with immunization using outer membrane proteins, thus allowing for the possibility for development of a recombinant vaccine. However, prioritizing the selection and testing of antigens from the protective outer membrane extract remains a challenge. Because A. marginale is an obligate intracellular pathogen, surface proteins that mediate adhesion to host cells, primarily red blood cells (RBCs), are functionally relevant vaccine candidates. With some exceptions, the proteins that bind RBCs remain unknown. To address this gap, a phage display library expressing 66 A. marginale proteins was screened to identify adhesins for bovine RBCs. Of the screened proteins, 73% were eliminated due to poor binding to RBCs. Several potential adhesins were identified, including Msp1b and OmpA, which are known adhesions for bovine RBCs and tick cells, respectively. Additionally, Mlp3, Am779, Msp3, and Omp13 met the criteria as RBCs adhesins and may serve as high priority vaccine candidates for future testing