Bernardo J, Brink H F, Simons E R
Department of Medicine, Boston University School of Medicine, Massachusetts 02118.
J Cell Physiol. 1988 Jan;134(1):131-6. doi: 10.1002/jcp.1041340116.
An important characteristic of the functional differentiation of the blood monocyte is the development of its capacity to recognize and respond to stimuli. This ability is mediated to a large extent by specific receptor glycoproteins located on the cell surface. Stimulation of mononuclear phagocytes via these receptors results in a rapid rise in intracellular Ca++ concentration, accompanied or followed by a change in membrane potential, generation of oxidative products, degranulation, and effector functions such as phagocytosis, aggregation, or locomotion. While the development of these characteristics is difficult to characterize in vivo, several investigators have demonstrated in vitro changes in these cells that correlate with the development of effector function. To examine the mechanisms of specific membrane-stimulus interactions of monocytes as they differentiate into macrophage-like cells, we studied the responses of human monocytes and of monocytes incubated in serum-containing medium for up to 96 hr to the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP). Freshly isolated monocytes exhibited little change in transmembrane potential following stimulation with an optimal concentration of peptide and underwent a significant increase only after 48 hr in culture. While constant resting intracellular Ca++ concentrations were maintained during the culture period, intracellular Ca++ levels following fMLP stimulation increased with with incubation in serum, for up to 96 hr. In contrast, fMLP-induced respiratory burst activity increased from 0 to 24 hr in culture; it remained elevated at 48 hr but declined again by 96 hr. Incubation of the cells for 24 hr increased their random (unstimulated) motility in modified Boyden chambers but did not alter the cells' directed (chemotactic) response to fMLP in comparison to the response of freshly isolated monocytes. Peptide binding to the cells did not increase during the incubation period, indicating that an increase in receptor number or in affinity for fMLP was not responsible for the enhanced responsiveness to fMLP as incubation time increased. These studies indicate that incubation of monocytes in serum-containing medium leads to a complex, altered series of responses to fMLP that correlate with the differentiation of the original monocytes in vitro and may relate to the in vivo differentiation of monocytes to macrophages.
血液单核细胞功能分化的一个重要特征是其识别和响应刺激能力的发展。这种能力在很大程度上由位于细胞表面的特异性受体糖蛋白介导。通过这些受体刺激单核吞噬细胞会导致细胞内Ca++浓度迅速升高，随之或随后伴有膜电位变化、氧化产物生成、脱颗粒以及吞噬作用、聚集或运动等效应功能。虽然这些特征在体内难以表征，但一些研究人员已在体外证明这些细胞的变化与效应功能的发展相关。为了研究单核细胞分化为巨噬细胞样细胞时特异性膜刺激相互作用的机制，我们研究了人单核细胞以及在含血清培养基中培养长达96小时的单核细胞对趋化肽甲酰甲硫氨酰亮氨酰苯丙氨酸（fMLP）的反应。新鲜分离的单核细胞在用最佳浓度的肽刺激后跨膜电位变化很小，仅在培养48小时后才出现显著增加。在培养期间细胞内Ca++浓度保持恒定，但fMLP刺激后的细胞内Ca++水平随着在血清中孵育时间的延长而增加，长达96小时。相比之下，fMLP诱导的呼吸爆发活性在培养0至24小时内增加；在48小时时保持升高，但在96小时时再次下降。细胞孵育24小时增加了它们在改良博伊登小室中的随机（未刺激）运动能力，但与新鲜分离的单核细胞的反应相比，并未改变细胞对fMLP的定向（趋化）反应。在孵育期间肽与细胞的结合没有增加，这表明随着孵育时间的增加，对fMLP反应性增强并非由于受体数量增加或对fMLP的亲和力增加。这些研究表明，将单核细胞在含血清培养基中孵育会导致对fMLP的一系列复杂、改变的反应，这些反应与原始单核细胞在体外的分化相关，并且可能与单核细胞在体内向巨噬细胞的分化有关。
