Local immune response to larvae of Rhipicephalus microplus in Santa Gertrudis cattle

Area of Science:

• Veterinary Immunology
• Parasitology
• Cattle Genetics

Background:

• Tick infestations pose significant economic challenges in cattle farming.
• Understanding the host immune response is crucial for developing effective tick control strategies.
• Santa Gertrudis cattle exhibit varying degrees of natural resistance to ticks.

Purpose of the Study:

• To investigate the local immune cell populations at tick larval attachment sites in cattle with differing tick resistance levels.
• To identify potential cellular markers associated with tick resistance or susceptibility in cattle.
• To explore the role of specific immune cells in the host response to early-stage tick infestation.

Main Methods:

• Skin biopsies were collected from Santa Gertrudis cattle after 25 weekly tick infestations.
• Immunohistochemistry was used to quantify immune cell infiltration (CD3+, CD4+, CD8+, CD25+, gamma delta T cells, neutrophils, eosinophils) at larval attachment sites.
• Monoclonal antibodies (mAbs) against CD45 and CD45 RO antigens were used to assess leukocyte presence.
• Intra-epidermal vesicles at attachment sites were analyzed for predominant cell types.

Main Results:

• A trend of increased CD3+, CD4+, CD8+, CD25+, gamma delta T cells, and neutrophils was observed at attachment sites in susceptible cattle compared to resistant cattle.
• Significant differences were found for gamma delta T cells and CD4+ cells, with higher counts in susceptible animals.
• Neutrophils predominated in vesicles of susceptible cattle, while eosinophils were more prevalent in resistant cattle.
• Leukocyte staining with mAbs for CD45 and CD45 RO was higher in susceptible cattle.

Conclusions:

• Some cellular immune responses at tick attachment sites may not contribute to tick protection in cattle.
• CD45 and CD45 RO antigens, or CD45 genotyping, show potential as biomarkers for predicting cattle tick resistance or susceptibility.
• Further research could lead to diagnostic tools for selective breeding of resistant cattle.