In vitro phagocytosis and killing of Corynebacterium equi by alveolar macrophages of foals.

The research looked at the ability of alveolar macrophages (a type of immune cell in the lung) in young foals to engulf and kill Corynebacterium equi bacteria. The findings revealed that while the macrophages’ ability to consume bacteria decreases with age, their actual success in killing the consumed bacteria doesn’t significantly change.

Examination and Collection of Samples

• The study started with collecting bronchoalveolar lavage (a technique for collecting samples from the lungs) from three healthy foals repeatedly over a range of age from 6 to 63 days.
• This allowed researchers to obtain alveolar macrophages, immune cells from the lungs, for testing.

Phagocytosis and Bactericidal Assays

• The researchers then conducted phagocytosis assays, which measure the ability of cells to engulf particles, and bactericidal assays, which measure the ability of these cells to kill bacteria.
• These tests were done on Corynebacterium equi bacteria coupled with alveolar macrophages in a ratio of 10 bacteria to 1 macrophage, incubated in a medium containing 1% heat-inactivated rabbit anti-C equi serum.

Findings

• After incubation, over 90% of alveolar macrophages had ingested at least one bacterium, with each macrophage on average possessing around 9.4 bacteria.
• However, when the same experiment was repeated using heat-inactivated pooled normal horse serum instead of rabbit serum, only about 24% of alveolar macrophages had ingested at least one bacterium, and each macrophage contained only about 0.8 bacteria on average.
• Despite these findings, the bactericidal – or bacteria-killing – activity of the macrophages didn’t significantly change with the age of the foals, ranged from 21 to 61 days.
• Moreover, even after a 4-hour in-vitro incubation period, around 75% of the ingested C. equi remained viable, indicating a relative inefficiency of the macrophages to kill the ingested bacteria.

Conclusion

• The study concluded that, while the phagocytic ability of alveolar macrophages decreased with the age of the foals, the actual ability to kill the ingested bacteria remained relatively constant.
• This understanding could provide valuable insights for further research into veterinary microbiology and immunology, particularly regarding foals and diseases caused by Corynebacterium equi.