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Changes in peripheral blood leucocytes of sheep experimentally infected with Mycoplasma agalactiae
Mariarosaria Marinaro1, Grazia Greco2, Elvira Tarsitano2
1Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy.
Abstract:
Contagious agalactia is a serious disease of small ruminants affecting mainly mammary glands, joints and eyes. In sheep, the main aetiological agent is Mycoplasma agalactiae (Ma) whose abilities to persist in the target organs are known. Since there is no information on the effect of acute and chronic Ma infection on circulating leucocytes, the present study was designed to monitor granulocytes, monocytes, T and B lymphocytes, by flow cytometry, in female lactating sheep nasally infected with Ma. A profound depletion of leucocytes was observed from day 5 to day 34 post infection (p.i.). In particular, while the granulocytes returned to baseline levels by day 12 p.i., the monocytes remained significantly low until day 20 p.i. The infection caused a prolonged depletion of peripheral T lymphocytes (both CD4(+) and CD8(+)) while B lymphocytes remained unaltered throughout the study. Mycoplasma agalactiae was detected by real-time PCR in several anatomical sites (ear, nose and milk) from day 2-5 p.i. until the end of the study (i.e., day 50 p.i.) while a transient bacteraemia was observed from day 5 to day 12 p.i. The leucopenia observed following intranasal Ma infection is likely due to leucocyte infiltration within the target organs.
Insights
Mycoplasma agalactiae (Ma) infection in sheep causes significant leucopenia, impacting T lymphocytes and monocytes. This leucocyte depletion is linked to the pathogen
Area of Science:
- Veterinary Immunology
- Infectious Diseases
- Small Ruminant Health
Background:
- Contagious agalactia, caused by Mycoplasma agalactiae (Ma), severely affects sheep mammary glands, joints, and eyes.
- The persistence of Ma in target organs is known, but its effect on circulating leukocytes during acute and chronic infection remains uncharacterized.
Purpose of the Study:
- To investigate the impact of acute and chronic Mycoplasma agalactiae infection on circulating leukocytes in lactating sheep.
- To monitor changes in granulocytes, monocytes, T lymphocytes (CD4+ and CD8+), and B lymphocytes using flow cytometry.
Main Methods:
- Female lactating sheep were intranasally infected with Mycoplasma agalactiae.
- Leukocyte populations were analyzed by flow cytometry at various time points post-infection.
- Mycoplasma agalactiae presence was confirmed using real-time PCR in different anatomical sites and blood.
Main Results:
- A profound leucopenia was observed from day 5 to day 34 post-infection.
- Granulocytes returned to baseline by day 12, while monocytes remained low until day 20.
- Prolonged depletion of peripheral T lymphocytes (CD4+ and CD8+) occurred, whereas B lymphocytes were unaffected. Ma persisted in ear, nose, and milk until day 50, with transient bacteraemia from day 5 to 12.
Conclusions:
- Intranasal Mycoplasma agalactiae infection induces significant and prolonged leucopenia in sheep.
- The observed leucopenia is likely attributed to leukocyte infiltration into infected target organs.
- This study provides novel insights into the immunological response to Ma infection in small ruminants.
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