Modulation of human polymorphonuclear neutrophil functions by alpha 1-acid glycoprotein

Alpha 1-acid glycoprotein potentiates lipopolysaccharide-induced secretion of interleukin-1 beta, interleukin-6 and tumor necrosis factor-alpha by human monocytes and alveolar and peritoneal macrophages

Although the physiological role of alpha 1-acid glycoprotein (AGP), an acute-phase protein, is poorly understood, several lines of evidence support a modulatory action on the immune response. In this study, we investigated the effect of AGP on the production of interleukin (IL)-1 beta, IL-6 and tumor necrosis factor (TNF)-alpha by human monocytes, macrophages and the monocytic THP-1 cell line. AGP significantly enhanced (2- to 7-fold) the production of these cytokines in monocytes induced by suboptimal concentrations of lipopolysaccharide [E. coli lipopolysaccharide (LPS): 100 ng/ml] in serum-free conditions, whereas it had little or no effect in the absence of LPS. The potentiating effect of AGP was inhibited by specific antibodies. It was concentration dependent and the greatest enhancement was observed with 250-500 micrograms/ml. Moreover, AGP only potentiated the effect of suboptimal concentrations of LPS. AGP did not alter the time course of LPS-induced IL-1 beta, IL-6 or TNF-alpha secretion. AGP acts as a co-inducer and could also potentiate cytokine secretion triggered by Neisseria meningitidis LPS and muramyl dipeptide. The glycan moiety of AGP did not seem to be involved in its potentiating effect, since both its major glycoforms and asialo-AGP potentiated the effect of LPS to the same extent as native AGP. Possible differences in the effect of AGP according to cell maturation were investigated using isolated human macrophages: AGP potentiated LPS-induced cytokine production by both peritoneal and alveolar macrophages. These data suggest that AGP can modulate monocyte/macrophage functions, thereby contributing to the amplification and regulation of immune and inflammatory responses.

Analysis of the five glycosylation sites of human alpha 1-acid glycoprotein

Orosomucoid (OMD) contains complex bi-, tri- and tetra-antennary glycan chains. Subfractionation of OMD into three molecular variants using concanavalin A lectin chromatography is based on variations in these complex structures. Standard h.p.l.c. profiles have been developed to analyse the percentage and distribution of the glycoforms present at each glycosylation site in OMD and its molecular variants. The ability to quantify the glycoforms present at each site allows us to extend the earlier results of others and resolve the remaining questions concerning the glycan structures of these variants. Most significantly, the proportions of bi-, tri- and tetra-antennary chains differ at each site for the three molecular variants. The most strongly retained variant from concanavalin A is uniquely capable of possessing biantennary chains at all five sites, whereas the unretained variant is completely devoid of biantennary chains. Only glycosylation site II of the five present is 100% biantennary in the retained and weakly retained variants. In addition, the two gene products of OMD were differentially glycosylated. Molecular masses of the glycoforms were verified by matrix-assisted u.v. laser desorption mass spectrometry. On the basis of the site distribution of oligosaccharides in the variants, efforts were made to understand the factors that control the processing of the carbohydrate chains in OMD. The results indicate that the 'site-directed' model of processing offers the most consistent explanation for the structures seen at the individual glycosylation sites of OMD.

Properties of four acute phase proteins: C-reactive protein, serum amyloid A protein, alpha 1-acid glycoprotein, and fibrinogen

Four plasma proteins, referred to as positive acute phase proteins because of increases in concentration following inflammatory stimuli, are reviewed: C-reactive protein (CRP), serum amyloid A protein (SAA), alpha 1-acid glycoprotein (AAG), and fibrinogen. The CRP and SAA may increase in concentration as much as 1000-fold, the AAG and fibrinogen approximately twofold to fourfold. All are synthesized mainly in the liver, but each may be produced in a number of extrahepatic sites. The role of cytokines in induction of the acute phase proteins is discussed, particularly the multiple functional capabilities of interleukin-6 (IL-6). Other cytokines that regulate acute phase gene expression and protein synthesis include IL-1, tumor necrosis factor alpha, interferon gamma, as well as other stimulatory factors and cofactors. The physicochemical characteristics of each protein are reviewed together with the molecular biology. For each protein, the known biological effects are detailed. The following functions for CRP have been described: reaction with cell surface receptors resulting in opsonization, enhanced phagocytosis, and passive protection; activation of the classical complement pathway; scavenger for chromatin fragments; inhibition of growth and/or metastases of tumor cells; modulation of polymorphonuclear function; and a few additional diverse activities. The role of plasma SAA is described as a precursor of protein AA in secondary amyloidosis; other functions are speculative. AAG may play an immunoregulatory role as well as a role in binding a number of diverse drugs. In addition to clot formation, new data are described for binding of fibrinogen and fibrin to complement receptor type 3. Finally, the concentration of each protein is discussed in a wide variety of noninfectious and infectious disease states, particularly in connective tissue diseases. The quantification of the proteins during the course of various acute and chronic inflammatory disorders is useful in diagnosis, therapy, and in some cases, prognosis.

Effect of canine surfactant protein (SP-A) on the respiratory burst of phagocytic cells

Cells obtained from bronchoalveolar lavage, or neutrophils of peripheral blood of dog, were incubated with the canine surfactant-associated protein A (SP-A). A significant decrease of the production of superoxide anion was observed after subsequent stimulation with phorbol-12-myristate-13-acetate (PMA) as measured by the lucigenin-dependent chemiluminescence (CL). Several other proteins used for control experiments did not decrease lucigenin-dependent CL, indicating a specific effect of SP-A on phagocytes. Treatment of SP-A with collagenase prior to incubation with neutrophils destroyed the depleting effect on oxygen radical production of PMA-stimulated cells. We propose that SP-A acts as a regulatory factor of the respiratory burst of alveolar macrophages and neutrophils in the lungs. The inhibitory effect of SP-A is down-regulated by collagenase released from stimulated alveolar macrophages.