Chemotaxis of horse polymorphonuclear leukocytes to N-formyl-L-methionyl-L-leucyl-L-phenylalanine.

This article investigates the chemotactic response of horse polymorphonuclear leukocytes (PMN) to the peptide N-Formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) commonly produced by prokaryotic organisms. It finds that FMLP is a weak chemotactic agent but can elicit responses after activating the complement system in a similar manner to zymosan.

Methods

• Two distinct types of PMN from horse blood were isolated for this experiment. The first type was isolated using sedimentation and isotonic lysis resulting in a PMN population with approximately 25% lymphocytes. The second type employed density gradient techniques for a nearly pure PMN yield.
• Then the peptide FMLP, representing the peptides produced by prokaryotic organisms, was introduced to the isolated leukocytes as a chemoattractant.

Findings

• The research found that FMLP was only effective as a chemoattractant for PMN at high concentration levels (10(-4) M).
• However, the researchers noted that when serum was preincubated with FMLP concentrations as low as 10(-8) M, the serum succeeded in attracting horse PMN, but this activity was not observed when heat-inactivated serum was used.
• According to the researchers, this suggests that FMLP has the ability to activate the complement system enabling the production of PMN chemoattractants, akin to zymosan, another commonly studied chemoattractant.
• The team also discovered that a combination of FMLP and zymosan didn’t bring about a more potent effect than zymosan alone, indicating that FMLP’s primary contribution is arguably its ability to initiate the complement system rather than to act as a direct chemoattractant.

Conclusion

• The research concludes that while FMLP is a weak chemoattractant for horse polymorphonuclear leukocytes, its capability to activate the complement system triggering the production of PMN chemoattractants is significant.