Priming of human neutrophils with N-formyl-methionyl-leucyl- phenylalanine by a calcium-independent, pertussis toxin-insensitive pathway

Abstract

Resting neutrophils may be “primed” to augmented effector function, eg, superoxide (O2-) production in the respiratory burst, upon a second stimulation with a variety of soluble agonists including formylated methionyl-leucyl-phenylalanine (FMLP) and phorbol myristate acetate (PMA). At priming concentrations of FMLP (5 x 10(-9) mol/L) that did not initiate O2- generation, two metabolic activities were noted: (1) approximately a threefold increase in the baseline intracellular calcium (Ca++i) level, that was not dependent on extracellular Ca++, and (2) a rapid rise in intracellular pH that was blocked by 5-(N,N- dimethyl) amiloride (DA), that had no effect on the Ca++i response to priming. Furthermore, there were no significant increases in inositol metabolites in cells primed and stimulated with FMLP compared with cells receiving the stimulating dose of FMLP alone and pretreatment with pertussis toxin (PT) (before the addition of the priming -5 x 10(- 9) mol/L dose of FMLP), whereas abolishing the response to FMLP during the second stage of stimulation, had (1) no effect on FMLP-primed cells subsequently stimulated with PMA, and (2) only partially ablated the rise in Ca++i initiated with FMLP. That FMLP priming involved distinctive processes to those of the well characterized FMLP-coupled Ca++-dependent activation cascade was shown by the full priming effect attained in a Ca++-free buffer, which did not sustain an O2- response to a second-stage FMLP stimulation, but sustained a primed response to PMA. These data demonstrate that FMLP primes human neutrophils by a Ca++-independent and PT-insensitive pathway, offering a functional model for studying heterogeneous FMLP receptor-coupled reactions.

Decoupling of Intracellular Calcium Signaling in Granulocytes After Exhaustive Exercise

“…The increases in chemoattractant induced Ca 2+ transients may reflect an activated or primed state of the neutrophils. The phenomena of an enhanced stimulus induced response of granulocytes after pre-incubation with low-concentration of various agonists that do not evoke any detectable response is referred to as priming [10]. Priming may account for alterations in calcium signalling observed in granulocytes of patients with rheumatoid arthritis [6].…”

Immunomodulatory Role of Neuropeptides in the Cornea

“…Depending on the timepoint or receptor type, VIP may have different effects on developing cDCs, inducing an inhibitory or immunogenic/mature cDC phenotype [ 376 , 377 , 378 ]. VIP primes the oxidative response of neutrophils to formyl-methionyl-leucyl-phenylalanine (FMLP) and phorbol myristate acetate (PMA) [ 379 , 380 ]. VIP has autocrine functions in mast cells that produce VIP and histamine through the classical IgE-mediated pathway, and VIP can also stimulate the release of histamine by mast cells, leading to inflammatory effects [ 381 , 382 ].…”