Effect of cyclic AMP on release of lysosomal enzymes from phagocytes

A comparative analysis of macrophage activation in C57B1/6 mice treated with inflammatory compounds or bearing Lewis lung carcinoma

The different percentages of acid hydrolases released by peritoneal macrophages obtained from C57B1/6 mice injected i.m. with talc, carrageenan or 3LL cells, and also the demonstration that hydrolase secretion from in vitro macrophage monolayers of tumor-bearing mice undergoes a further increase when zymosan is added to the culture, strongly suggest the possibility that more than one membrane surface receptor is involved in the triggering of lysosomal enzyme release. Furthermore, there is evidence from the reported results that, besides immune complexes, neoplastic cells or their metabolic product(s) could act as inducers of the lysosomal enzyme secretion by macrophages.

Cyclic nucleotides and catecholamines in rheumatoid arthritis

A controlled cross over study on the effect of fasting on cyclic nucleotide and catecholamine excretion was carried out in 12 female RA patients. They were hospitalized during a control and fasting period. The fasting period started with 3 days of habituation to hospital conditions, followed by 7 days of total fasting. Thereafter followed 3 days of realimentation. The control period was in every respect identical with the fasting period, with the exception of food intake. All medication was stopped when the patients were admitted to the hospital. The urinary concentrations of cAMP, cGMP, E and NE were monitored daily. The clinical status of the subjects was evaluated every second day using Ritchie's clinical index. Clinical and laboratory measures of inflammatory activity remained unaltered during the control period, but improved significantly during fasting. Excretion of cAMP and cGMP was low during the control period when compared with published normal levels. The cAMP/cGMP ratio in urine was normal, however. The urinary levels of E and NE were normal in the control period, but increased significantly during fasting. Excretion of cAMP decreased during fasting, while urinary cGMP levels decreased initially, but rose to prefasting levels towards the end of the fast. The cAMP/cGMP ratio increased during the first days of the fast, with a maximum on days 2 and 3. This increment coincided in time with the greatest rate of improvement in clinical joint activity.

Control of the production of oxygen intermediates of human polymorphonuclear leukocytes and monocytes by beta-adrenergic receptors

The control by beta-adrenergic receptors of the production of oxygen radicals by zymosan-stimulated human polymorphonuclear leukocytes (PMN) and monocytes (M phi) was studied in vitro by means of chemiluminescence. In addition we asked whether PMN and M phi exhibit differential sensitivity to beta-adrenergic stimulation. For beta-adrenergic stimulation we applied fenoterol ranging from 10(-5) to 10(-9) M x 2.7. We found a dose-dependent suppression of the production of oxygen radicals, the ID50 being approximately 10(-6) M both for PMN and M phi. By assessment of lactic dehydrogenase release a cytotoxic effect of the drug could be ruled out. When incubated together with the beta-adrenergic antagonist propranolol at 10(-6) and 10(-7) M the suppression effect of fenoterol could be reversed in dose-dependency. Preincubation with fenoterol revealed that the inhibitory action on M phi persisted, in contrast, no such suppression could be verified with PMN. Our findings indicate the control of the production of oxygen intermediates of human PMN and M phi by beta-adrenergic stimulation. Furthermore, selective functional modulation of resting PMN and M phi by beta-adrenoceptors is suggested. These effects may be of importance in vivo, in particular since fenoterol was applied in pharmacological doses.

Response of lung enzyme activities in rabbits following short-term exposure to n-hexane: correlation between morphological and biochemical changes

The activity of lactate dehydrogenase, beta-glucuronidase, glucose-6-phosphate dehydrogenase, acid and alkaline phosphatase was studied in lung homogenate from New Zealand rabbits exposed to 3000 p.p.m. of n-hexane 8 h per day for 8 days of filtered air. In hydrocarbon-treated animals all enzymes examined, except alkaline phosphatase, were markedly increased. The biochemical changes correlated well with the morphological changes and the results of cytological evaluation of bronchopulmonary lavage. It is suggested that high values in lung lysosomal enzymes from treated rabbits reflect the acute inflammation whilst the increase in lung glucose-6-phosphate dehydrogenase may depend upon reparative process subsequent to n-hexane-induced lung damage.

Ibuprofen in canine endotoxin shock

The participation of prostaglandins in the physiologic alterations of endotoxin shock has been well established with the aid of prostaglandin synthetase inhibitors. Our study was designed to investigate the potential of ibuprofen, a highly specific cyclooxygenase inhibitor, to reverse the hemodynamic and acid base abnormalities of canine endotoxin shock. Mean blood pressure fell to 49.8 +/- 6.6 mm Hg in dogs given endotoxin by 5 min after injection, and remained below 83 mm Hg for the duration of the 120-min observation period. In animals given endotoxin followed by ibuprofen, a similar initial drop of systemic blood pressure was seen, but it subsequently recovered to 150.2 +/- 4.1 mm Hg by 120 min (P less than 0.001). Cardiac index increased in animals given ibuprofen (2.3 +/- 0.28 liter/m2 per min) compared with animals given endotoxin alone (1.0 +/- 0.09 liter/m2 per min) by termination of the experiment. The arterial pH dropped in endotoxin treated animals to 7.18 +/- 0.03 by 120 min. Ibuprofen prevented the acidosis, the final pH in ibuprofen and endotoxin treated animals measuring 7.36 +/- 0.01. We conclude that ibuprofen protects against the hypotension, acidosis, and depression of cardiac index of canine endotoxin shock.

Elevated serum levels of lactoferrin and eosinophil cationic protein in schizophrenic patients

The serum levels of lactoferrin, eosinophil cationic protein (ECP), lysozyme and beta 2-microglobulin have been measured in schizophrenic patients in an attempt to elucidate the activity and turnover of neutrophil and eosinophil granulocytes, macrophages/monocytes and lymphocytes, respectively. Serum-lactoferrin and serum-ECP levels were significantly (P less than 0.001) higher in the patient group as compared to healthy controls in contrast to blood cell counts and serum-lysozyme and serum- beta 2-microglobulin levels which all were within normal limits. The results were not affected by anti-psychotic therapy. A significant correlation was found between serum-ECP and serum-lactoferrin levels which may suggest a common underlying cause of the elevated levels. The findings suggest an increased eosinophil and neutrophil activity and/or turnover in schizophrenia and may have a bearing on the well-known altered inflammatory response associated with this syndrome.

Prostaglandins in gingiva of patients with periodontal disease

Prostaglandin E and F were measured simultaneously by radioimmunoassay in extracts of gingiva of patients with chronic periodontal disease. The mean values of PGE and PGF in 27 gingival samples were 42.2 +/- 4.9 and 52.6 +/- 6.8 pmol/gm wet tissue weight, respectively. The correlation coefficient (r) between the two groups of PGs was a positive 0.42, significant at P less than 0.05.

The role of complement in the function of the monocyte - macrophage system

In parallel to the behavior of many agents that activate complement via the alternative pathway and can stimulate macrophages to secrete lysosomal enzymes we investigated the interaction of mouse peritoneal macrophages cultured in a serum-free medium with various stimuli such as zymosan, polyanions, collagen type II, and immune complexes prepared from tetanus toxoid and pooled human anti-tetanus toxoid F(ab)2. All these stimuli induced the release of hydrolytic enzymes from macrophage in culture. The release was time and dose dependent and is not associated with loss of the cytoplasmic enzyme lactate dehydrogenase or any other sign of cell death. The mechanism of macrophage activation by these various agents is unknown. Macrophages have surface receptors for Fc and C3b with the capacity to bind immune complexes or C3b, respectively, and this is followed by activation of the cells. Activation via the Fc part can be excluded in these experiments. The possibility therefore arose that macrophages might be stimulated by endogenous C3 via the C3b receptor, since it is known that all the substances mentioned above can activate C3. To confirm this hypothesis we tried to inhibit this reaction by using an anti-C3-Fab preparation. There was hardly any detectably enzyme release after adding the anti-C3-Fab (dose dependent) together with the various stimuli to the macrophages. An unrelated Fab preparation showed no inhibitory effect. Furthermore, incubation of macrophages and the stimuli together with beta 1H and C3bINA abolished the effect to activate the macrophages. The observations now presented focus attention to the possibility that endogenous C3 could play a role in the stimulation of mouse peritoneal macrophages by various activators of the alternative pathway.

Dissociation of intracellular lysosomal rupture from the cell death caused by silica

The relationship between intracellular lysosomal rupture and cell death caused by silica was studied in P388d(1) macrophages. After 3 h of exposure to 150 mug silica in medium containing 1.8 mM Ca(2+), 60 percent of the cells were unable to exclude trypan blue. In the absence of extracellular Ca(2+), however, all of the cells remained viable. Phagocytosis of silica particles occurred to the same extent in the presence or absence of Ca(2+). The percentage of P388D(1) cells killed by silica depended on the dose and the concentration of Ca(2+) in the medium. Intracellular lyosomal rupture after exposure to silica was measured by acridine orange fluorescence or histochemical assay of horseradish peroxidase. With either assay, 60 percent of the cells exposed to 150 mug silica for 3 h in the presence of Ca(2+) showed intracellular lysosomal rupture, was not associated with measureable degradation of total DNA, RNA, protein, or phospholipids or accelerated turnover of exogenous horseradish peroxidase. Pretreatment with promethazine (20 mug/ml) protected 80 percent of P388D(1) macrophages against silica toxicity although lysosomal rupture occurred in 60-70 percent of the cells. Intracellular lysosomal rupture was prevented in 80 percent of the cells by pretreatment with indomethacin (5 x 10(-5)M), yet 40-50 percent of the cells died after 3 h of exposure to 150 mug silica in 1.8 mM extracellular Ca(2+). The calcium ionophore A23187 also caused intracellular lysosomal rupture in 90-98 percent of the cells treated for 1 h in either the presence or absence of extracellular Ca(2+). With the addition of 1.8 mM Ca(2+), 80 percent of the cells was killed after 3 h, whereas all of the cells remained viable in the absence of Ca(2+). These experiments suggest that intracellular lysosomal rupture is not causally related to the cell death cause by silica or A23187. Cell death is dependent on extracellular Ca(2+) and may be mediated by an influx of these ions across the plasma membrane permeability barrier damaged directly by exposure to these toxins.

Pinocytosis in human synovial cells in vitro. Evidence for enhanced activity in rheumatoid arthritis

Human synovial tissue cells in monolayer can be shown to take up and digest a soluble protein, horseradish peroxidase (HRP). Uptake of HRP was linear with increasing concentrations of substrate and cell protein and with time for up to 4 h. Low temperature (4 degrees C), and sodium fluoride, an inhibitor of glycolysis were the most effective metabolic inhibitors of endocytosis. In addition, colchicine, an inhibitor of microtubule assembly, and yeast mannan, an inhibitor of mannose-specific receptors, reduced HRP uptake. Synovial cells from patients with rheumatoid arthritis (RSC) demonstrated a statistically significantly higher rate of endocytosis (247 +/- 107 ng HRP/100 micrograms cell protein per 2 h.) than cells from control, nonrheumatoid patients (NSC) (100 +/- 80 ng HRP/100 micrograms cell protein per 2 h). Thus, it is possible to discriminate RSC from NSC by their quantitatively different rates of endocytosis. Digestion of HRP by synovial cells is statistically significant by 6 h after uptake. A faster initial rate of digestion was seen in RSC. Over the first 6--8 h of incubation 42% of the endocytosed HRP was still cell-associated in RSC and 67% remained in NSC cultures. However, by 24 h 20--30% of endocytosed HRP was found in both types of cultures. These results indicate that endocytosed molecules may accumulate more rapidly in RSC and persist within their lysosomes for a longer time than in NSC. The quantitative determination of enhanced endocytosis by RSC compared with NSC suggests that this increased activity may have a role in the pathological function of synovial tissue in rheumatoid arthritis.

Anti-inflammatory activity of amine cyanoboranes, amine carboxyboranes, and related compounds

Amine cyanoboranes and amine carboxyboranes (boron analogs of alpha-amino acids) were shown to inhibit inflammation. The analogs effectively blocked general inflammation, induced arthritis, and the writhing reflex associated with inflammation pain, while the inflammation associated with pleurisy was marginally inhibited. The boron analogs were shown in vitro to inhibit the release of lysosomal enzymes from liver and polymorphonuclear neutrophils. Furthermore, prostaglandin synthesis was blocked by these agents at a low concentration, i.e., 10(-6) M. Liver oxidative phosphorylation processes also were uncoupled by these agents, but the migration of polymorphonuclear neutrophils was unaltered at 10(-4) M. The elevation of cyclic adenosine monophosphate levels in polymorphonuclear neutrophils correlated positively with in vivo antiarthritic activity. Initial studies in rodents demonstrated that these boron analogs can be used at safe therapeutic doses.

Induction of cell infiltration and acid hydrolase release into the peritoneal cavity of mice

An injection of thioglycollate into the peritoneal cavity of mice produced a peak of exudate at 4 h, a peak of total leukocytes at 24 h when the predominant cell was the polymorphonuclear neutrophil, and a secondard macrophage phase beginning 2--3 days after thioglycollate. The release of N-acetylglucosaminidase (EC 3.2.1.30) into the peritoneal fluid paralleled the macrophage phase. The amount of enzyme released was related to the dose of thioglycollate. Neither zymosan (400 micrograms) nor endotoxin (30 micrograms) produced a marked inflammatory response when injected into the peritoneal cavity.

Enzymes of the mast cell granule

Rat mast cell granules contain a spectrum of enzymes as established by histochemical techniques and subcellular fractionation. However, 35% of the beta-glucuronidase, 30% of the beta-D-galactosidase, 14% of the beta-hexosaminidase and all of the acid phosphatase is not available for immunologic release from purified rat serosal mast cells, suggesting the presence of nonsecretory lysosomes containing these acid hydrolases. On the other hand, immunologic release of the majority of chymase, beta-hexosaminidase, beta-glucuronidase, beta-D-galactosidase, and arylsulfatase A occurs in parallel with histamine and thereby localizes these substances to the rat mast cell secretory granule. A molecular model of the secretory granule in the resting mast cell can now be constructed in which heparin proteoglycan is the granule matrix to which chymase and probably other proteins are ionically bound. Inhibition of chymase by serotonin stored in its active site and of chymase and acid hydrolases by their interaction with heparin probably occurs. Histamine is stored by ionic linkage to carboxyl groups of protein and heparin. Micromolar amounts of heparin glycosaminoglycans, histamine, serotonin, chymase, beta-D-hexosaminidase, beta-glucuronidase, and arylsulfatase A in secretory granules of 10(6) mast cells are 0.7--1.3 x 10(-3), 70--220 x 10(-3), 0.9--28 x 10(-3), 0.2--0.5 x 10(-3), 0.9--2.7 x 10(-6), 0.1--0.3 x 10(-6) and less than 8 x 10(-6), respectively. In addition, the total protein available for calcium ionophore-induced release from 10(6) rat mast cells is about 60 microgram, indicating that less than 50% of the granule protein can be accounted for. Recognition that mast cell secretory granules contain acid hydrolases indicates that they are modified lysosomes; their special intracellular and extracellular functions are dictated by the associated novel constituents and the stimulus for activation.

Exocytosis by macrophage polykarya: an ultrastructural study

Macrophage polykarya selectively secrete their lysosomal contents directly into the extracellular space or into the intracytoplasmic membranous labyrinth. Fusion of the lysosomal membrane with the plasmalemma or with the cytoplasmic labyrinth results in the release of the lysosomal contents. The labyrinth, however, was shown to be essentially similar to the plasmalemma, hinting that comparable mechanisms are involved in both instances. The process of secretion is unrelated to motility and phagocytosis and may be important in the extracellular degradation of biological material.

The effect of fasting on plasma cyclic adenosine-3', 5'-monophosphate in rheumatoid arthritis

Cyclic adenosine-3', 5'-monophosphate (cAMP) may influence important mechanisms in the inflammatory process, and fasting has been claimed to be clinically beneficial in rheumatoid arthritis (RA). A study was therefore designed to measure the concentrations of plasma cAMP in RA patients not undergoing drug treatment during a control and a fasting period. Twelve female RA patients were hospitalized for two 14-day periods and investigated in a crossover study. Clinical and laboratory variables of inflammatory activity were assessed during both periods. During the control period the concentrations of cAMP in plasma were slightly below the lower normal limit, with no significant change throughout the period. The clinical and laboratory variables of inflammatory activity were unchanged during the same period. In the fasting period, the prefasting level of plasma cAMP was significantly higher than on the corresponding day in the control period. During 7 days of total fasting the plasma cAMP concentrations decreased significantly. The clinical and laboratory variables of inflammatory activity decreased significantly from the start to the end of fasting. High prefasting plasma cAMP concentrations were associated with improvement in clinical inflammatory activity. A decrease in plasma cAMP concentrations during fasting in RA patients is in contrast to the findings in obese and healthy subjects previously reported.

Lithium as an immunologic adjuvant

Lithium, an adenylate cyclase inhibitor, stimulates a variety of in vitro indices of immune function, including proliferation of lymphocytes in response to mitogens, rosette formation by T-cells and phagocytosis by macrophages. Lithium enhances these immunologic responses at concentrations comparable to those achieved in patients receiving lithium for treatment of manic-depressive disorders. Lithium may prove to have important therapeutic applications as an immune adjuvant, particularly in immune deficiency states associated with excessive C-AMP production.

Effect of bioflavonoids on lysosomal acid hydrolases and lysosomal stability in adjuvant-induced arthritis

In rats with adjuvant-induced arthritis, the effect of (+)-catechin (CA) and 0-(beta-hydroxyethyl) rutosides (HR) on the activity of certain lysosomal acid hydrolases, viz., beta-glucuronidase, beta-N-acetyl glucosaminidase and cathepsin D in serum, liver, kidney and spleen and the stability of liver lysosomes was studied. The activity of these enzymes in arthritic tissues and serum increased significantly. The total activity of beta-glucuronidase in the lysosome-rich fraction from arthritic liver was appreciably decreased, while its release was significantly increased. These results demonstrate the fragility of lysosomes in arthritic tissues. Administration of CA or HR to the arthritic animals was found to have a prophylactic action by stabilizing liver lysosomes and reducing the free lysosomal enzyme activities in serum, liver, kidney and spleen. CA was more effective than HR.

Induction of plasminogen activator secretion in macrophages by electrochemical stimulation of the hexose monophosphate shunt with methylene blue

Resident peritoneal macrophages were obtained from untreated mice and were cultured in medium 199 with or without 5% acid-treated fetal bovine serum. Three hours after harvesting, redox compounds--i.e., methylene blue, methyl viologen, or nitro blue tetrazolium--were added to the cultures of adherent cells. After 1 hr, the cells were washed and culturing was continued in the absence of redox compounds. The effects of the redox compounds were tested by assaying for hexose monophosphate (HMP) shunt activity and for plasminogen activator secretion, and the results were compared with the effects induced by phagocytic stimuli. Methylene blue caused a concentration-dependent stimulation of the HMP shunt, whereas methyl viologen and nitro blue tetrazolium were ineffective. Shunt stimulation by methylene blue was followed, after a lag of 2-4 days, by plasminogen activator secretion. The rate of secretion was dependent on the methylene blue concentration used. Methyl viologen and nitro blue tetrazolium were again ineffective, whereas phagocytosis of zymosan or sheep erythrocytes, which stimulates the HMP shunt, induced plasminogen activator secretion at rates similar to those induced by methylene blue. These results add further evidence to our hypothesis that the HMP shunt-dependent metabolic burst is involved in macrophage activation. Because methylene blue mimics the action of zymosan it appears that shunt stimulation by itself initiates the activation process independently of phagocytosis.

Macromolecular, anionic pulmonary permeability factor

Aqueous extracts of fresh or acetone-powdered calf lung have been found to contain a factor which increases the permeability of the microcirculation when injected into the skin of rats. This permeability factor, which is not found in similar extracts of muscle or kidney, was concentrated by Amicon ultrafiltration at a molecular weight range of between 50,000 and 100,000 daltons and via isoelectric focusing at an IEP of pH 4.2. After preparative acrylamide gel electrophoresis, this permeability factor was homogeneous by electrophoretic criteria and in SDS acrylamide gel electrophoresis had a molecular weight of approximately 82,000 daltons. This apparently homogeneous permeability factor from lung was inhibited by pepstatin, and yet possessed no acid proteolytic activity against any substrate. Its activity was completely inhibited by pretreatment of the animals with antihistamines. This pepstatin-inhibitable permeability factor was found largely in the lysosomal fraction of fresh lung and could also be obtained by extraction of large amounts of alveolar "washout" macrophages. Since macrophages, during phagocytosis, are known to leak significant quantities of their lysosomal contents, the fact that one of these components is a material which could release histamine from mast cells and thereby increase locally the permeability of the microcirculation may be of importance in the defense system of the lung.

Macrophage polykarya

Multinucleated giant cells are commonly found in a wide variety of inflammatory reactions. They are formed at sites of tissue injury by fusion of freshly exuded monocytes, the rate of fusion being dependent on a range of extracellular and intracellular factors. Electron miscroscopy shows that the pooled components of the fused monocytes are not randomly dispersed in the syncytium, but are highly reorganized into a functioning unit. In addition, histochemical and biochemical profiles of cell populations containing these polykarya display a range of metabolic activities, including DNA synthesis, which, on occasions, is followed by successful mitotic division and the formation of polyploid daughter cells. Fusion results in the loss of some surface receptors which in turn interferes with the phagocytic performance of polykarya, which is generally less pronounced than their mononuclear precurses. In addition, polykarya are not as actively motile as macrophages although phenomena of contact inhibition are less obvious. On the other hand, the multinucleate giant cells display prominent exocytosis which may aid in the degradation of extracellular material. The properties of macrophage polykarya contrast with macrophage homokarya produced in vitro. The latter are actively phagocytic, do not synthesize DNA, and have a longer half-life than the syncytia produced in chronic inflammatory reactions. It may well be that the polykarya in such reactions are not true homokarya.

Cyclic nucleotides in joint fluid in rheumatoid arthritis and in Reiter's syndrome

Levels of cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) have been investigated in joint fluid in inflammatory arthropathies. A disturbed balance between cAMP and cGMP due to a depressed level of cAMP was found in rheumatoid arthritis (RA) and Reiter's syndrome, in comparison with patients with osteoarthritis. No correlation could be demonstrated between the absolute levels of cAMP or cGMP and the degree of local inflammatory activity, white cell count, or lysosomal enzyme activity in the joint fluid. Intra-articular injection of epinephrine showed just as good an effect on local pain as betamethasone (Cellestona), but the steriod reduced the swelling more effectively. An increase in intracellular levels of cAMP at 20 min was observed following injection of epinephrine with a slight change in cGMP. Intra-articular injection of dibutyryl-cAMP (db-cAMP) produced a marked easing of local pain and swelling in each of the 4 patients so treated. It is concluded that stimulation of the beta-adrenergic system or injection with db-cAMP may be beneficial in rheumatoid inflammation.

Role of phagocytosis in the activation of macrophages

Macrophages were obtained by peritoneal lavage from untreated mice or from mice which had received either Brewer's thioglycollate broth or a suspension of streptococcus A cell walls intraperitoneally 4 days before. 3 h after harvesting, adherent cells from untreated mice were allowed to phagocytose zymosan, formaldehyde-treated sheep erythrocytes, or latex beads. Phagocytosis was stopped after 1 h and culture was continued for up to 10 days. Phagocytosis of zymosan or sheep erythrocytes triggered the immediate release of lysosomal glycosidases, stimulated the synthesis of cellular lactate dehydrogenase, and induced the delayed production and secretion of plasminogen activator . No such changes were observed upon phagocytosis of latex. Although all three particles used were phagocytosed, only zymosan and sheep erythrocytes stimulated glucose oxidation via the hexose monophosphate shunt. Similar findings were obtained in macrophages elicited with streptococcus A cell walls after zymosan phagocytosis. Thioglycollate-elicited macrophages, however, which were already secreting lysosomal hydrolases and plasminogen activator, could not be activated further by zymosan. The results of this study show that macrophages become activated after phagocytosis of particles that stimulate the activity of their hexose monophosphate shunt. The triggering event appears to be the burst of shunt activity itself or shunt-related biochemical reactions rather than phagocytic uptake per se or particle-dependent complement activation by the alternative pathway. Once initiated, macrophage activation proceeds independently of the intracellular fate of the ingested material .

Comparative studies of erythrophagocytosis in the rabbit and human vitreous

The ultrastructural changes which occurred during red cell degradation in the vitreous were studied in rabbit and human eyes. The major pathway for red cell lysis was extracellular in both species, and this type of haemolysis was probably induced by the unfavourable environment in the vitreous and by age changes in the red cells themselves. The released red cell debris was then phagocytosed by invading macrophages. Intracellular lysis also occurred within the cytoplasm of large macrophages after ingestion of whole red cells by the phagocytes. Thus inflammatory cells were always ultimately involved in both forms of red cell lysis in the vitreous. Intracellular lysis appeared to be more common in human cases of recurrent intravitreal haemorrhage associated with intravitreal new vessel formation. In addition, a higher proportion of young macrophages was observed in the inflammatory cell exudates of recurrent haemorrhages, suggesting that macrophage turnover was more rapid in these cases.

Prostaglandins as regulators in cellular immunity

Guinea-pig peritoneal macrophages have been shown to generate substantial concentrations of E-type prostaglandins during culture in vitro. Partially purified lymphokine preparations stimulate PGE production by macrophages. Exogenous PGE1 and PGE2 are potent inhibitors of lymphocyte activation and secretion of lymphokines causing lymphocyte mitogenesis and macrophage migration inhibition. Also indomethacin augments the secretion of these lymphokines in vitro. It is therefore suggested that production of PGE by macrophages provides a physiological mechanism for the regulation of lymphocyte activation in reactions of delayed hypersensitivity.