Two functional domains in the phagocyte membrane glycoprotein Mo1 identified with monoclonal antibodies

Granulocytes from patients genetically deficient in the leukocyte glycoprotein family, Mo1, LFA-1, and Leu-M5 (P150,94), have defective complement receptor type III (CR3) activity as well as abnormal adhesion-dependent functions such as spreading, chemotaxis, and phagocytosis. To determine the contribution of the Mo1 heterodimer deficiency to the various functional aberrations observed in deficient granulocytes, we mapped the functional domains of Mo1 using several monoclonal antibodies to this molecule. In addition to iC3b binding, two granulocyte adhesion functions were examined: Cell spreading on plastic coverslips and chemotaxis. One monoclonal antibody to Mo1, 44, inhibits all three functions. Other monoclonal antibodies (903, Leu-15, and OKM10) inhibit iC3b binding to granulocytes but have no effect on cell spreading and/or chemotaxis. Another antibody, 904, has no significant inhibition of iC3b binding but inhibits spreading on plastic and chemotaxis. These studies suggest the presence of two functional domains in Mo1: one involved in iC3b binding and the other in enhancing certain granulocyte adhesion-dependent functions.

Vasoactive intestinal polypeptide is synthesized in anterior pituitary tissue

Previous studies have suggested that vasoactive intestinal polypeptide (VIP) is involved in regulation of PRL secretion within the pituitary gland. In order to determine whether VIP is synthesized in anterior pituitary tissue, we performed three experiments. In all experiments, anterior pituitaries were obtained from male rats. The tissue was then labeled by incubation in leucine-free minimum essential medium containing [3H]leucine, 14 microCi/ml. In Exp I, the labeled tissue was homogenized, centrifuged, and the supernatant was chromatographed on Sephadex G-50F. The fractions indicated a large peak of counts near the void volume and another peak coeluting with VIP. These latter fractions were pooled and subjected to reverse phase HPLC. Fractions from the HPLC indicated: a protein peak, VIP immunoreactivity, and maximum counts immunoprecipitated by anti-VIP serum at the retention time of synthetic porcine VIP. Exp II consisted of perifusion of labeled pituitary quarters over a 120-min period followed by an additional 60 min in the presence of 56 mM KCl. During this latter period of KCl depolarization, a large amount of 3H-labeled material was secreted. These fractions were then chromatographed on Sephadex G-50F, and the fractions coeluting with [125I]porcine VIP were subjected to immunoprecipitation with anti-VIP serum. In addition, all fractions from the Sephadex column were assayed for VIP, and the only activity was at the elution volume of [125I]porcine VIP. In Exp III, the pituitary labeling procedure included 3.6 X 10(-5) M cycloheximide. Subsequently, the tissue was perifused and the perifusate collected during the 60-min 56 mM KCl perifusion phase was pooled and immunoprecipitated with anti-VIP serum. No immunoprecipitable counts were obtained. These experiments indicate that anterior pituitary tissue synthesizes VIP on the basis of the HPLC profile and immunoprecipitation with specific anti-VIP antiserum. These results, in addition to other studies by our laboratory and others, suggest that intrapituitary VIP may be an important regulator of anterior pituitary hormone secretion, particularly PRL.

Human recombinant granulocyte-macrophage colony-stimulating factor increases cell-to-cell adhesion and surface expression of adhesion-promoting surface glycoproteins on mature granulocytes

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to inhibit migration of mature granulocytes and to enhance their antibody-dependent cellular cytotoxicity. We found that human recombinant GM-CSF also enhanced granulocyte-granulocyte adhesion and increased by two- to threefold the surface expression of Mo1 and LeuM5 (P150, 95), two members of a family of leukocyte adhesion molecules (Leu-CAM). Increased Mo1 surface expression occurred within 15 min at 37 degrees C and was maximal at the migration inhibitory concentration of 500 pM. One-half maximal rise in the expression of Mo1 on the cell surface occurred at 5 pM. The chemotactic peptide f-Met-Leu-Phe produced a comparable rise in surface Mo1 with one-half maximal expression occurring at 7 nM. Both GM-CSF and f-Met-Leu-Phe produced optimal granulocyte-granulocyte adhesion at 500 pM and 100 nM, respectively. This adhesion-promoting effect induced by either stimulus was inhibited by a mouse monoclonal antibody directed against Mo1 antigen. These data indicate that GM-CSF promotes cell-to-cell adhesion, presumably through enhanced expression of leukocyte adhesion molecules. This mechanism may explain, in part, the known effects of GM-CSF on the function of mature granulocytes.

Antisera to vasoactive intestinal polypeptide inhibit basal prolactin release from dispersed anterior pituitary cells

Vasoactive intestinal polypeptide (VIP) has been identified in hypothalamic tissue, is secreted into hypophysial portal blood, and stimulates prolactin (PRL) release in vivo and in vitro. It has been proposed, therefore, that VIP is a physiologic PRL-releasing factor. In this study, we confirm that VIP stimulates PRL release from rat pituitary cells in vitro, and demonstrate that an anti-VIP antiserum blocks VIP-induced PRL secretion. Surprisingly, the anti-VIP antiserum inhibited basal PRL secretion from rat pituitary cells in 3 separate experiments. Data from these experiments were pooled, as the responses were similar, revealing basal PRL release of 10.7 +/- 1.3 ng rPRL/10(5) cells (X +/- SE), while anti-VIP antisera significantly inhibited release to 4.4 +/- 0.6 ng rPRL/10(5) cells (p less than 0.001). PRL release in incubates containing control non-immune sera did not differ from basal release, 8.1 ng rPRL/10(5) cells. A further control experiment was conducted wherein cells were incubated with an anti-ACTH antiserum, representing another hyperimmune serum, which had no effect on PRL secretion. These data suggest that VIP, in addition to its possible role as a hypothalamic-derived PRL-releasing factor, may play a role within the pituitary as a regulator of basal PRL secretion.

p150/95, Third member of the LFA-1/CR3 polypeptide family identified by anti-Leu M5 monoclonal antibody

Monoclonal antibody (mAb) anti-Leu M5 reacts with a two-chain molecule composed of a 150-kDa alpha subunit noncovalently associated with a 95-kDa beta subunit and probably is specific for an epitope on the 150-kDa alpha chain. This p150/95 antigen is the third member of a family of polypeptides sharing a common 95-kDa beta chain, which includes the lymphocyte function-associated antigen LFA-1 (p177/95) and complement receptor CR3 (Mo1/MAC-1/OKM1; p165/95) antigens. Sequential immunoprecipitation with anti-p95 beta chain mAb specifically removed the antigens detected by anti-LFA-1, anti-CR3 and anti-Leu M5 mAb. Certain patients with recurrent bacterial infections are genetically deficient in expression of the LFA-1 and Mo1 antigens, and have impaired granulocyte function. Granulocytes from a patient with this disease also failed to react with anti-Leu M5. Stimulation of normal granulocytes with f-Met-Leu-Phe, C5a-desArg, or calcium ionophore resulted in increased expression of Mo1 and Leu M5 antigens on the cell surface, but did not significantly increase expression of LFA-1 antigen. In functional assays, anti-Leu M5 did not inhibit T cell-mediated or natural killer cell-mediated cytotoxicity. In addition, anti-Leu M5 neither inhibited the binding of complement-coated particles to CR1 or CR3 nor did it affect the binding of EC3dg to neutrophils (CR4). These studies clearly indicate that the p150/95 antigen recognized by the anti-Leu M5 antibody is a structurally distinct member of the LFA-1/CR3 family.

The modulated expression of Mo5, a human myelomonocytic plasma membrane antigen

Mo5 is a 94-kd protein antigen expressed by human peripheral blood monocytes, neutrophils, and by all bone marrow myeloperoxidase-positive myeloid precursors (promyelocytes, myelocytes, metamyelocytes, and bands). Mo5 is borne by the malignant cells of 74% of patients (N = 27) with acute monocytic leukemia (French-American-British [FAB] group M4, M5), and 50% of patients (N = 38) with acute granulocytic leukemia (FAB M1, M2, and M3). Nonmyeloid cells in peripheral blood and bone marrow are Mo5-negative. The surface expression of Mo5 by myeloid cells is modulated by several experimental conditions: Exposure of neutrophils to calcium ionophore (1 mumol/L, 37 degrees C, ten minutes) under conditions resulting in degranulation of specific granules produces a three- to fourfold increase in the plasma membrane density of Mo5 antigen. This suggests that, in neutrophils, there is an intracellular pool of Mo5 antigen, which may be associated with specific granules, and that granule-associated Mo5 is translocated to the plasma membrane upon degranulation. Conversely, incubation of monocytes, neutrophils, U-937, and Mo5-positive leukemia cells in medium containing anti-Mo5 monoclonal antibody results in a significant decrease in surface Mo5 expression. This loss of surface Mo5 is a rapid, temperature-dependent process (occurring within 30 minutes at 37 degrees C) that is produced by divalent anti-Mo5 immunoglobulin [F(ab')2 but not F(ab)]. After down-modulation, Mo5 is reexpressed by monocytes within 48 hours. Mo5 is therefore a human myelomonocytic differentiation antigen whose expression is modulated up or down depending on the nature of extracellular stimuli.

Gastroduodenal inflammation in patients with non-ulcer dyspepsia. A controlled endoscopic and morphometric study

Proper control and quantitation are important in the accurate evaluation of gastroduodenal inflammation in dyspeptic patients without ulcers or erosions as proved by endoscopy. The endoscopic findings and the gastroduodenal mucosal inflammatory cell count in 31 patients with non-ulcer dyspepsia were compared with an age-matched group of 32 healthy controls. Endoscopy revealed similar mucosal changes and in similar frequency in both groups. Differential mucosal inflammatory cell count showed a statistically significant (P less than 0.001) increase in the neutrophil count in the gastric body, antrum, and duodenal cap of the dyspeptic group, as well as a slight but significant (P less than 0.05) increase in the round cell and eosinophil count of the duodenal mucosa alone. No correlation was found between the endoscopic changes and an increase in neutrophil count above a normal level determined by the healthy controls. However, an endoscopically normal mucosa was more likely to be associated with a normal neutrophil count. Active inflammation of the gastroduodenal mucosa likely accounts for the symptoms in patients with non-ulcer dyspepsia.

Studies of basal and stimulated gastric acid output in Jordanian male and female patients and controls

To further elucidate geographic variations in acid secretion, basal and maximal acid output, corrected for body weight, was studied in age-matched groups of 86 patients with duodenal ulcer, 26 patients with non-ulcer dyspepsia and 31 normal controls in Jordan. The acid output was significantly higher in duodenal ulcer subjects, but in patients with non-ulcer dyspepsia it was the same as in controls. There were important sex differences: males secreted significantly more acid than females in all groups; and increased acid secretion in duodenal ulcer patients was due to hypersecretion in male patients only, there being no significant difference in acid secretion in females of any study group. Twenty-six percent of the duodenal ulcer subjects in the age-matched groups were acid hypersecretors, and these were all males. Weight had no effect on acid output. When compared to most studies from other parts of the world, it is apparent that females with duodenal ulcer in Jordan have less increase in acid secretion. Impaired mucosal resistance is probably more important than acid hypersecretion in the pathogenesis of duodenal ulcer in Jordan.

Increased expression of an adhesion-promoting surface glycoprotein in the granulocytopenia of hemodialysis

To identify the mechanisms accounting for hemodialysis-induced granulocytopenia, we undertook quantitative kinetic studies of a granulocyte-adhesion-promoting surface glycoprotein (Mo1). In eight patients undergoing maintenance hemodialysis, there was a fivefold increase in the mean cell-surface expression of Mo1 within 15 minutes after the start of dialysis with a new cuprophane membrane. The peak increase in surface Mo1 coincided with the maximal drop in neutrophil count and with the peak rise in the plasma levels of the complement-activation products C5a desArg and C3a desArg. During dialysis on a membrane being reused for the fifth time, no significant complement activation, no increase in Mo1 expression, and no change in neutrophil count were seen. C5a desArg (but not C3a desArg) induced a comparable increase in Mo1 expression on normal granulocytes in vitro at concentrations similar to those measured in vivo. Chemotactic peptide-induced granulocyte aggregation (a reflection of increased cell-to-cell adhesiveness) was specifically blocked by mouse monoclonal antibodies to Mo1 in vitro. These data suggest that the increased expression of Mo1 on granulocytes in vivo is in part mediated by C5a (and C5a desArg). The quantitative increase in granulocyte-surface Mo1 may provide a mechanism for initiating leukoaggregation, sequestration of granulocytes, and neutropenia during hemodialysis.

Complement C3 receptors: structure and function

Significant progress has been made during the past few years toward elucidating the structure and function of various C3 receptors. Better understanding of the biochemical basis of the immune adherence phenomenon has been achieved. The availability of polyclonal and monoclonal antibodies to C3 receptors allowed more accurate studies of the cellular distribution of these receptors. Finally, advances in our knowledge of the functional properties of the C3 receptors and their relationship to specific cell surface molecules was facilitated by recognition of a patient deficient in various receptor-mediated functions. All together these developments will soon make it possible to describe in detail the molecular events involved in the modulation of complement receptor coupled cell functions.

Subcellular localization of the large subunit of Mo1 (Mo1 alpha; formerly gp 110), a surface glycoprotein associated with neutrophil adhesion

Mo1 alpha (formerly gp 110) is a neutrophil glycoprotein whose deficiency is associated with abnormalities in several neutrophil functions, including defects in adherence, chemotaxis, and phagocytosis. Examination of whole cells and subcellular components by the use of both immunological and electrophoretic techniques demonstrated that Mo1 alpha was located primarily in the specific granules but that a small portion was present in the plasma membrane, where it is exposed to the extracellular environment and can bind to anti-Mo1 antibody. During degranulation, Mo1 alpha is translocated from the specific granules to the plasma membrane, resulting in a 5-10-fold increase in the surface expression of this glycoprotein. These findings plus previous work suggest that plasma membrane-associated Mo1 alpha is needed for a normal interaction between neutrophils and underlying surfaces, and raise the possibility that the increase in surface adhesiveness of neutrophils that have discharged their specific granules might be due in part to the increase in the amount of Mo1 alpha in the plasma membranes of these degranulated cells.

Deficiency of a leukocyte surface glycoprotein (LFA-1) in two patients with Mo1 deficiency. Effects of cell activation on Mo1/LFA-1 surface expression in normal and deficient leukocytes

Mo1, a phagocyte surface glycoprotein heterodimer, is involved in a number of phagocyte adhesion functions such as binding and ingestion of serum-opsonized particles, zymosan-induced degranulation, and superoxide generation. Deficiency of this antigen in humans has been associated with increased susceptibility to recurrent bacterial infections. The beta subunit of Mo1 is shared by another surface glycoprotein named LFA-1, which is involved in lymphocyte proliferation, cytolytic T cell, and natural killing activities. Two unrelated patients with Mo1 deficiency were found to be deficient in LFA-1 as well as in the common beta subunit. Investigation of lymphocyte functions in these two patients revealed normal mixed leukocyte culture-generated cytolytic T cell and natural killing activities and significantly reduced proliferative response to phytohemagglutinin. LFA-1-deficient cells also proliferated in response to soluble antigen and different alloantigens. These responses were partially blocked by anti-LFA-1 antibody. Whereas LFA-1 was undetectable by immunofluorescence and immunoprecipitation on the patients' resting T cells, significantly reduced (approximately 5% of normal) but detectable amounts of the heterodimeric LFA-1 antigen were found on mitogen and alloantigen-activated T cells. On granulocytes, Mo1 surface expression was also dependent on the state of cellular activation. The amount of surface Mo1 present on resting normal granulocytes increased by 3-10-fold following exposure to stimuli that induced degranulation, suggesting the presence of a major intracellular pool for this antigen. Analysis of subcellular fractions from granulocytes showed that intracellular Mo1 is located primarily in the specific granule fraction. Activated granulocytes had little or no increase in their surface expression of LFA-1 antigen. Deficient granulocytes had significantly increased numbers of Mo1 antigen expressed on the surface following stimulation with calcium ionophore (1 microM). However, the amount expressed continued to be significantly reduced compared with normal cells. Quantitation of surface Mo1 on granulocytes exposed to calcium ionophore (1 microM) showed that both parents in one family but only the mother in the other family had significantly reduced levels of Mo1, suggesting heterogeneity in the inheritance of this disorder. Whereas LFA-1 deficiency on lymphocytes was associated with normal alloantigen-induced cytolytic T cell and natural killing activities in these two patients, functions which were in part dependent on small amounts of detectable LFA-1 antigen, the Mo1 deficiency state led to significant defects in phagocyte adhesion functions. Hence, the clinical symptoms associated with this combined deficiency state reflect a more profound phagocyte than lymphocyte disorder.

Abnormalities of polymorphonuclear leukocyte function associated with a heritable deficiency of high molecular weight surface glycoproteins (GP138): common relationship to diminished cell adherence

Investigations of polymorphonuclear leukocyte (PMN) function were performed in a 5-yr-old white female with delayed umbilical cord separation, impaired pus formation, and a severe defect of PMN chemotaxis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated an almost total deficiency of a high molecular weight glycoprotein(s) (GP138) in the granule and membrane fractions of the patient's cells, and NaB3H4-galactose oxidase labeling demonstrated the absence of a major glycoprotein complex on the surface of her PMNs. Monoclonal antibodies (MAb) were employed in flow cytometry experiments to demonstrate that two previously characterized glycoproteins (Mo1 and LFA1) were undetectable on the surface of the patient's PMNs and monocytes. Immunoprecipitation of 125I-labeled patient cells with subunit specific MAbs confirmed that the alpha-subunits of Mo1 (155 kD) and LFA1 (177 kD) and their common beta-subunit (94 kD) were totally deficient. Functional analyses of patient PMNs demonstrated severe impairment of adherence- and adhesion-dependent cell functions including spreading, aggregation, orientation in chemotactic gradients, antibody-dependent cellular cytotoxicity, and phagocytosis of particles (Oil-Red-0-paraffin, zymosan) selectively opsonized with C3-derived ligands. Patient PMNs demonstrated a normal capacity to rosette with IgG or C3b-coated sheep erythrocytes, but rosette formation with C3bi-coated erythrocytes was profoundly diminished. Adhesion-independent functions including shape change, N-formyl-methionyl-leucyl-3H-phenylalanine binding, and O-2 generation or secretion elicited by soluble stimuli were normal. Membrane fluidity, surface charge, and microtubule assembly were also normal. These findings provide new evidence that critical PMN surface glycoproteins are required to facilitate multiple adhesion-dependent cellular functions of the inflammatory response.

Biosynthesis and postsynthetic processing of human C3b/C4b inactivator (factor I) in three hepatoma cell lines

Human factor I is a two-chain plasma glycoprotein composed of disulfide-linked 50,000- and 38,000-dalton subunits. Analysis of its biosynthesis and postsynthetic processing demonstrated that factor I is synthesized as a single chain precursor (pro-I) that undergoes glycosylation and limited proteolysis to generate the native protein. One of three human hepatoma cell lines, HepG2 , secreted factor I predominantly (70-90%) in a single chain pro-I form. The other cell lines secrete factor I predominantly in its two chain native form. The defect in conversion of pro-I to I in HepG2 was protein specific since other multichain proteins, derived from single chain precursors, the third, fourth, and fifth components of complement were processed normally. Further analysis of the inefficient pro-I to I conversion by HepG2 revealed that Xenopus oocytes injected with HepG2 mRNA secreted factor I in a predominantly two-chain form. In addition, the apparent sizes of native factor I, transferrin, and alpha-1-antitrypsin secreted by the three hepatoma lines differed due to differences in postsynthetic processing.

Deficiency of a surface membrane glycoprotein (Mo1) in man

Deficiency of a granulocyte surface glycoprotein of 150,000-D had been associated with defective C3- and IgG-dependent phagocytosis in a patient with recurrent bacterial infections. By using monoclonal antibodies, we found that this patient's granulocytes, monocytes, and null cells were deficient in Mo1 (equivalent to OKM1 and Mac-1), a cell surface molecule consisting of two noncovalently linked glycoproteins of 155,000 and 94,000 D. The 155,000-D subunit is closely associated with the human complement receptor that recognizes C3bi and/or a further degradation product termed C3dg (C3bi receptor); the 94,000-D subunit has been shown to be shared, on normal cells, by two other surface membrane glycoproteins: lymphocyte function-associated antigen-1 (LFA-1) and P-150, 95. Both subunits of Mo1 were deficient on the patient's granulocytes as determined by immunoprecipitation with subunit-specific monoclonal antibodies as well as fluorescence analysis. Mol-deficient monocytes, like granulocytes, had defective C3-and IgG-dependent phagocytosis. Natural killing activity by the patient's peripheral blood leukocytes was normal. Mo1-deficient granulocytes and monocytes rosetted normally with sheep erythrocytes coated with C3bi. This rosetting was totally inhibited by a mixture of anti-Mo1 and anti-C3b (the major fragment of C3) receptor antibodies but not by either antibody alone. Since monoclonal antibodies to the 155,000-D subunit of Mo1 can inhibit C3bi receptor binding, immune phagocytosis, opsonized zymosan-induced degranulation, and superoxide generation by normal phagocytes (functions which are defective in Mo1-deficient cells), it appears likely that Mo1 deficiency may in part underlie the functional aberrations leading to recurrent bacterial infections in man.

Induction of granulocyte histaminase release by particle-bound complement C3 cleavage products (C3b, C3bi) and IgG

The interaction of opsonized particles with human granulocytes promotes a number of important biologic functions, including phagocytosis, superoxide generation, and release of a variety of enzymes, including histaminase. We have previously determined that histaminase release occurs via a C3-dependent process. Although fluid-phase C3b dimers can mediate release, the relative effects of particle-bound C3b and C3bi and of IgG have not been examined. In this report we demonstrate that particle-bound C3 deposited on activators of the alternative C pathway effected histaminase release in the absence of IgG. Particle-bound C3bi and C3b were both effective as mediators of histaminase release. The extent of release varied as a function of the activating surface on which C3 was deposited (zymosan C3b was considerably more potent than C3b bound to rabbit erythrocytes, which was slightly more potent than C3b bound to neuraminidase-treated sheep erythrocytes). In contrast, C3b or C3bi deposited on nonactivating surfaces (such as sheep erythrocytes) at inputs of up to 2,000,000 molecules per granulocyte failed to induce histaminase release unless IgG was also present. The ability of C3b bound to particles that serve as activators of the alternative pathway to induce histaminase release is apparently not the result of decreased susceptibility of C3b to proteolysis or to an increased binding affinity to the C3b receptor, but may relate to the interaction of other surface structures on activating particles with the PMN membrane.

Inhibition of phagocytosis of complement C3- or immunoglobulin G-coated particles and of C3bi binding by monoclonal antibodies to a monocyte-granulocyte membrane glycoprotein (Mol)

Events that lead to phagocytosis of complement (C3)- or IgG-coated particles after their interaction with specific cell surface receptors are poorly understood. Two mouse monoclonal antibodies (an IgM and an IgG2a) to a human granulocyte-monocyte surface membrane differentiation antigen (Mol) inhibited ingestion by granulocytes both of oil Red O particles opsonized with normal human serum or with IgG and of sheep erythrocytes sensitized with IgG. In addition, they specifically inhibited rosetting between phagocytes and sheep erythrocytes coated with C3bi, a fragment of the complement component C3, generated by cleaving C3b with C3b inactivator and beta IH protein. These monoclonal anti-Mol antibodies did not inhibit IgG Fc, C3b or C3d receptor-mediated binding of erythrocytes coated with the respective proteins. The Fab fragment of the IgG2a monoclonal antibody inhibited noncytotoxic enzyme release from granulocytes when these cells were stimulated with zymosan coated with C3bi. Electrophoretic transfer of polymorphonuclear leukocyte detergent lysates to nitrocellulose, followed by immunofixation with monoclonal antibody, showed that these antibodies were directed to a 155,000-mol wt glycoprotein. This surface membrane structure appears to be involved in Fc and C3 receptor-dependent phagocytosis and closely associated with the C3bi receptor.

Induction of granulocyte histaminase release by particle-bound complement C3 cleavage products (C3b, C3bi) and IgG

The interaction of opsonized particles with human granulocytes promotes a number of important biologic functions, including phagocytosis, superoxide generation, and release of a variety of enzymes, including histaminase. We have previously determined that histaminase release occurs via a C3-dependent process. Although fluid-phase C3b dimers can mediate release, the relative effects of particle-bound C3b and C3bi and of IgG have not been examined. In this report we demonstrate that particle-bound C3 deposited on activators of the alternative C pathway effected histaminase release in the absence of IgG. Particle-bound C3bi and C3b were both effective as mediators of histaminase release. The extent of release varied as a function of the activating surface on which C3 was deposited (zymosan C3b was considerably more potent than C3b bound to rabbit erythrocytes, which was slightly more potent than C3b bound to neuraminidase-treated sheep erythrocytes). In contrast, C3b or C3bi deposited on nonactivating surfaces (such as sheep erythrocytes) at inputs of up to 2,000,000 molecules per granulocyte failed to induce histaminase release unless IgG was also present. The ability of C3b bound to particles that serve as activators of the alternative pathway to induce histaminase release is apparently not the result of decreased susceptibility of C3b to proteolysis or to an increased binding affinity to the C3b receptor, but may relate to the interaction of other surface structures on activating particles with the PMN membrane.

Role of human factor I and C3b receptor in the cleavage of surface-bound C3bi molecules

Control of functions mediated by the third component of complement (C3) depends on the rate of generation and degradation of biologically active C3 fragments. To evaluate the mechanisms of degradation of active C3 fragments, the role of the control protein C3b/C4b inactivator (factor I) was investigated under conditions approximating those found in vivo, i.e. in the presence of plasma. The breakdown of human erythrocyte-bound C3bi molecules in serum or plasma was mediated only by factor I, since factor I-deficient or -depleted plasma was inactive until reconstituted with highly purified factor I. The rate of cleavage of C3bi bound to human erythrocytes by purified factor I was not affected by the presence or absence of beta 1H (factor H). The released breakdown product of C3bi has been shown to be C3c antigenically and on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Two different monospecific antibodies to the human C3b receptor totally abrogated factor I-mediated cleavage of cell-bound C3bi, suggesting that the C3b receptor (but not factor H) is required as an obligate cofactor. The rate of this C3b receptor-dependent, factor I-mediated cleavage of bound C3bi is strongly regulated by the surface to which C3bi is bound. Whereas C3bi bound to particulate nonactivators of the alternative complement pathway such as human erythrocytes is rapidly degraded by this mechanism, the rate of cleavage of C3bi bound to activators is significantly slower. These data suggest a physiologic role of C3b receptors in the degradation of biologically active C3 fragments deposited on host tissues. They also suggest that C3bi molecules on restricted surfaces are relatively stable and can thereby interact with complement C3 receptors in vivo.

Diverticular disease of the colon in Jordan

In a case review over a nine-year period, 35 patients were referred to the University Hospital with a variety of abdominal symptoms related to the gastrointestinal tract, were found to have diverticular disease of the colon. In a retrospective evaluation of 274 consecutive barium enemas performed at the same institute in patients aged 20 to 85 years, in a three-year period (1979 to 1981), colonic diverticula were found in 11 patients, giving incidence of 4 per cent; all positive enemas for diverticulosis in this group occurred in patients over the age of 40 years.

Low ionic strength or chemical cross-linking of monomeric C3b increases its binding affinity to the human complement C3b receptor

Quantitative studies of the interaction between a fragment of the third component of complement (C3b) and its receptor on human cells have been undertaken with a recently developed radioligand binding assay. Specific binding of fluid phase monomeric C3b was direct and saturable under low (mu = 0.0513) but not physiological (mu = 0.15) ionic strength. Dimeric C3b had a greater affinity for the C3b receptor at either ionic strength. Complexing of monomeric C3b with another protein (human IgG) did not result in increase in binding to human erythrocytes when compared with monomeric C3b alone. These data suggest that ionic forces are involved in C3b receptor-ligand interactions and that the stable C3b-receptor binding site is present in monomeric C3b. Furthermore they suggest that the greater affinity of dimeric or oligomeric C3b is a result of multimeric binding to preclustered C3b receptors. These findings provide an explanation for the relatively stable interaction of particle bound C3b and C3b receptor-bearing cells in the immune adherence reaction.

Complement (C3b) interaction with the human granulocyte receptor: correlation of binding of fluid-phase radiolabeled ligand with histaminase release

The interaction of C3b, the major cleavage product of C3, with its receptor on human granulocytes results in important biological functions, including phagocytosis, superoxide generation, and release of a variety of enzymes, including histaminase. We have determined the binding kinetics and isotherm of trypsin-generated fluid-phase dimeric C3b at both 0 degrees C and 37 degrees C using human polymorphonuclear leukocytes (PMN). At 37 degrees C the apparent number of receptors per cell was threefold greater than number at 0 degrees C (66,000 vs 21,000), and the affinity (Ka) was slightly less (3.5 X 10(7) M-1 vs 6 x 10(7) M-1). C3b dimer binding was specifically inhibited by a F(ab,)2 anti-C3b receptor antibody. C3b dimer induced histaminase release in a dose-dependent fashion at a concentration of 1 to 4 X 10(7) molecules/cell, whereas at lower concentrations a dose-dependent inhibition of opsonized zymosan-induced release was noted. These effects were independent of IgG. In contrast, C3b monomer failed to demonstrate measurable direct binding or to induce histaminase release. Histaminase release, however, did occur after incubation of PMN with affinity-linked monomer (anti-C3 F(ab')2-C3b complexes). Monovalent complexes did not affect release. Monomeric C3, C3c, and C3d were without effect; however, affinity-linked C3 and C3c did cause release.

Complement (C3b) interaction with the human granulocyte receptor: correlation of binding of fluid-phase radiolabeled ligand with histaminase release

The interaction of C3b, the major cleavage product of C3, with its receptor on human granulocytes results in important biological functions, including phagocytosis, superoxide generation, and release of a variety of enzymes, including histaminase. We have determined the binding kinetics and isotherm of trypsin-generated fluid-phase dimeric C3b at both 0 degrees C and 37 degrees C using human polymorphonuclear leukocytes (PMN). At 37 degrees C the apparent number of receptors per cell was threefold greater than number at 0 degrees C (66,000 vs 21,000), and the affinity (Ka) was slightly less (3.5 X 10(7) M-1 vs 6 x 10(7) M-1). C3b dimer binding was specifically inhibited by a F(ab,)2 anti-C3b receptor antibody. C3b dimer induced histaminase release in a dose-dependent fashion at a concentration of 1 to 4 X 10(7) molecules/cell, whereas at lower concentrations a dose-dependent inhibition of opsonized zymosan-induced release was noted. These effects were independent of IgG. In contrast, C3b monomer failed to demonstrate measurable direct binding or to induce histaminase release. Histaminase release, however, did occur after incubation of PMN with affinity-linked monomer (anti-C3 F(ab')2-C3b complexes). Monovalent complexes did not affect release. Monomeric C3, C3c, and C3d were without effect; however, affinity-linked C3 and C3c did cause release.