Abstract
To identify possible secretory determinants of impaired hyperadherence and stimulated migration of neonatal granulocytes (NGs), we performed correlative studies of: (a) specific granule content and exocytosis, (b) secretago-gue-mediated upregulation of f-met-leu-phe (fMLP) receptors, (c) the chemotactic induction of the adhesive glycoproteins Mac-1 alpha (complement receptor 3) and beta, and (d) morphometric assessments of specific (peroxidase negative) granule depletion following chemotactic stimulation. Lactoferrin (LF) content of NG suspensions (cord blood or peripheral blood cells) was profoundly diminished (mean +/- SD 51% +/- 18% of normal) as compared with healthy adult granulocytes (AGs). Despite diminished cellular content, LF release by NG suspensions in response to fMLP was comparable to that of AGs. In contrast, LF release by NG suspensions was significantly diminished in response to phorbol myristate acetate (PMA) or calcium ionophor A23187 and/or during stimulated cell spreading, experimental conditions promoting overall greater LF depletion than chemotactic stimuli. In addition, NGs demonstrated an impaired capacity to upregulate fMLP receptors in response to PMA or A23187 when tested under the same experimental conditions. Baseline expression of the adhesive glycoproteins Mac-1 alpha and beta on NG surfaces was normal, but induction or upregulation of these proteins by chemotactic concentrations of fMLP, C5a as well as secretory (high) concentrations of PMA and A23187, was significantly diminished as compared with AGs. In contrast, chemotactic induction of the surface expression of the complement receptor-1 (CR-1) on NGs was normal. An impaired induction of Mac-1 alpha or beta was directly related to an impaired enhancement of adherence of NG in response to fMLP over a chemotactically relevant concentration range (10(-10) to 10(-7) mol/L). Moreover, in blocking- incubation experiments using anti-Mac-1 alpha/beta monoclonal antibodies (MAbs), significantly less inhibition of adherence by these MAbs was evident with fMLP-stimulated NG as compared with AG suspensions. Under selected chemotactic conditions, ultrastructural assessments of NGs demonstrated diminished peroxidase-negative granule loss in association with diminished granule-membrane fusion and the “addition” of plasma membrane. These studies suggest that abnormal expression of multiple surface determinants derived from peroxidase- negative granules or other intracellular pools may contribute to deficient chemotaxis or other inflammatory functions of NGs.(ABSTRACT TRUNCATED AT 400 WORDS)
