Equine complement activation as a mechanism for equine neutrophil migration in Onchocerca cervicalis infections.

The research examines the role of equine complement activation in promoting neutrophil migration in horse infections caused by the Onchocerca cervicalis parasite. They found that no cell migration is stimulated by the parasite alone, but when combined with equine serum, there was a significant increase in neutrophil movement, indicating a potential role of the equine alternative complement pathway.

Experiment Overview

• The experiment started with the incubation of extracts of Onchocerca cervicalis (a horse parasite) with radiolabeled equine neutrophils. The researchers were trying to observe if the factors that promote neutrophil migration were derived from the parasite or maybe derived from host (the horse) after interaction with the parasite.
• They tested saline extracts from adult worms, uterine microfilariae, and skin microfilariae. However, they could not detect any stimulus for cell migration at any dosage tested. This highlights that the parasite itself does not directly cause neutrophil movement, suggesting the need for interaction with other host factors.

The Role of Equine Serum

• The study takes a significant turn when the parasite extracts are incubated with equine serum – a liquid part of the blood comprising proteins and antibodies. Suddenly, the neutrophil migration was notably stimulated.
• Further tests on the serum showed that this increased cell movement disappears if the equine serum is pretreated with 10 mM EDTA or heated at 50 and 56 degrees Celsius for 30 minutes. This suggests that some heat-sensitive, and EDTA-sensitive elements in the serum are crucial for neutrophil migration. As EDTA is known to interfere with the function of some metal-dependent proteins, this may indicate the involvement of such proteins.
• However, when the serum was treated with EGTA (made 10 mM with respect to Mg2+ ions), there was no reduction of neutrophil migration. Thus, the authors postulated that the equine alternative complement pathway could be responsible for the increased neutrophil movement. The alternative complement pathway is a part of the immune system, suggesting an immune response to the parasite.

Identifying the Neutrophil Stimulus

• Preliminary gel filtration of the activated equine serum suggested that though there was a neutrophil stimulus associated with a molecule similar to C5a (a protein involved in immune response), other complement or serum components could also be involved in this process.
• In conclusion, these findings demonstrate that the horse’s immune system interacts with the Onchocerca cervicalis parasite, creating a stimulus for neutrophil migration, a crucial step in the immune response. It further implies that the equine alternative complement pathway plays a vital role in this process.