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Intravenous injection of mice with soluble complexes of highly avid rabbit antibody to egg albumin, prepared by dissolution of equivalence precipitates in large quantities of antigen, resulted in a purely mesangial localization of the complexes. When animals received three injections of complexes per day for 1 day it was noted that precipitates dissolved in 80 times the equivalence amount of antigen produced slight mesangial changes. When such complexes were injected for 2 or 3 days, outright mesangiopathic glomerulonephritis was observed in an increasing proportion of the animals. Equivalent amounts of antigen alone did not produce lesions.

Repeated intravenous injections of egg albumin in rabbits produced small antigen-excess complexes and severe glomerulonephritis. Immunoglobulins and complement in the glomeruli were not clearly demonstrated by immunofluorescence; deposits were found to be sparse by electron microscopy. This study demonstrates that soluble immune complexes are responsible for the glomerular reaction. The apparent absence of deposits is thus not sufficient to exclude an immune complex pathogenesis.

Glomerular lesions were evaluated by light, electron, and immunofluorescence microscopy in rabbits given daily injections, for prolonged periods of time, of either 12.5 mg. of bovine serum albumin (BSA) (group I) or increasing doses of BSA, paralleling the immune response (group II). In animals clearing 12.5 mg. or more of BSA per day (excluding those dying of anaphylaxis or unknown causes), marked differences were noted in the incidence of membranous glomerulonephritis (GLN) (50 per cent in group I versus 15.4 per cent in group II), of crescentic GLN (none in group I versus 26.9 per cent in group II), and of mesangiopathic GLN (11.1 per cent in group I versus 30.8 per cent in group II). On the basis of these variations and immunofluorescence microscopy findinds, it is concluded that the occurrence of membranous GLN is favored by the presence in the circulation of small concentrations of soluble immune complexes, whereas crescentic GLN results from the presence of high concentrations of such complexes. When BSA injections were discontinued in group I animals having membranous GLN, the immune deposits were sequestered by membranous transformation so that they were not readily solubilized by injections of large amounts of BSA; one such animal developed crescentic GLN. The observation that BSA was difficult to detect in the lesions of mesangiopathic GLN suggests that this lesion results from the deposition of complexes formed at equivalence or in antibody excess.

To study the role of the fixed anionic sites of the glomerular capillary wall in protein filtration, the negative charges were neutralized in vivo. With systemic infusion of the polycation protamine sulfate, glomerular staining for polyanion was reduced and protein excretion increased by 154%. To avoid systemic side effects in subsequent studies, small doses of a polycation were infused directly into one renal artery. The contralateral kidney was infused with the vehicle solution. Albumin excretion from the experimental kidneys in the first 1-hr collection after infusing 0.5 mg protamine sulfate was 24.3 +/- 6.3 micrograms/min/kidney (N = 13; P less than 0.01). Albuminuria declined during the subsequent 3 hr with a second infusion inducing a second proteinuric response. The degree and longevity of the albuminuric response was correlated directly to the dose of protamine sulfate. The polycations hexadimethrine and poly-l-lysine also induced proteinuria. The increased protein excretion consisted of albumin; the excretion of nonalbumin protein was identical in the experimental and control kidneys. Hemodynamic factors did not explain the increase in proteinuria. Morphologically, the polycation-treated kidneys showed scanty foot process fusion and a decrease in free negative sites in the lamina rarae of the glomerular basement membrane. The results strongly support an important role for glomerular charge in preventing filtration of circulating plasma albumin.

The effect of heparin on the development and progression of a form of antiglomerular basement membrane nephritis was examined in the rat. Animals which received heparin before and throughout the period of immunological insult developed lesions which were as severe, and perhaps more severe, than rats which did not receive heparin. Inulin clearances were lower in heparin-treated animals than in untreated rats. Animals in both groups exhibited renal fibrin-fibrinogen deposition and had increased rates of urinary fibrin-fibrinogen related antigen excretion. These results indicate that heparin per se has no beneficial effect on the development of this form of glomerulonephritis in this species.

Rabbits were given injections of preformed complexes of purified goat antirabbit glomerular basement membrane antibody and rabbit antigoat immunoglobulin. When the animals were killed 24 hours later, examination of their kidneys revealed diffuse glomerulonephritis with widespread areas of localized loop necrosis, associated with extensive accumulations of polymorphonuclear leukocytes. By electron microscopy, accumulations of polymorphonuclear leukocytes in various degrees of disintegration were associated with areas of the basement membrane that appeared to be losing their structural integrity, suggesting that the damage to the membrane was brought about by the action of lysosomal enzymes. Reduction of the number of circulating polymorphonuclear leukocytes by pretreatment of the animals with nitrogen mustard completely prevented the lesions. Reduction of circulating complement levels by pretreatment of the animals with cobra venom factor prevented the occurrence of localized necrosis but allowed the development of the diffuse lesion.

Intravenous injections of mice three times a day for 3 days with soluble complexes of 3 mg. of moderately avid rabbit antibody to chicken egg albumin prepared by dissolution of equivalence precipitates in 80 times the equivalence amount of antigen resulted in a combined mesangial and loop localization of immune complexes. With complexes formed from antibody of low avidity, injected four times a day for 3 days, a predominately subepithelial loop deposition of complexes was observed. Complexes formed from moderately avid antibody gave rise to a mainly mesangiopathic glomerulonephritis, whereas low avidity complexes were associated with a diffuse glomerulonephritis. These results, in combination with those of the previous paper, successfully reproduce the basic form of the lesions seen in active immune complex disease by passive means and suggest that antibody avidity is a major determinant of the site of localization of immune complexes and therefore of the morphologic form of the resulting glomerulonephritis. The importance of these observations for our understanding of the pathogenesis of human immune complex disease is considered.

The concurrent administration of compound E at a daily dosage of 2 mg. per kg. to rabbits receiving daily intracutaneous injections of crystalline egg albumin markedly inhibited the development of anaphylactic hypersensitivity of the Arthus type. ACTH, when given at a similar dosage, produced a much less marked effect. Both hormones suppressed circulating antibody and as with the Arthus reaction, the suppression produced by compound E was much greater than that obtained with ACTH. When treatment with compound E was started following sensitization, there was a rapid decline in circulating antibody and, if the pretreatment serum antibody was low, there was also a progressive decrease in skin reactivity, becoming negative after 5 days of treatment. When the pretreatment serum antibody concentration was great, so that by the termination of treatment the antibody concentration was still above the level ordinarily sufficient for a maximal skin response, the Arthus reaction was unaffected by treatment. These considerations as well as the failure of compound E to inhibit the systemic passive Arthus reaction suggest that the inhibitory effect of compound E and ACTH on the development of experimental hypersensitivity results from the hormonal reduction of circulating antibody. Treatment with compound E had no effect on the rate of disappearance of circulating antibody in the passively immunized rabbit. This finding suggests that ACTH and compound E reduce circulating antibody by inhibiting antibody formation rather than by promoting antibody destruction. The question is raised as to whether the marked lymphoid atrophy produced by these hormones may be related to the interference with antibody production.

A histologic and quantitative immunologic study was made on a large group of rabbits injected intravenously with a single dose of crystallized bovine albumin and bled and sacrificed at various intervals after injection. Both cardiovascular and renal lesions were encountered in high incidence. The various stages in the development of these lesions were observed from their first appearance until their complete regression. The cardiac, vascular, and renal alterations were morphologically similar to those of rheumatic fever, polyarteritis nodosa, and acute glomerulonephritis, respectively, in man. In addition to those tissue changes ordinarily attributed to hypersensitivity, peculiar granulomatous lesions consisting of epithelioid and foreign body giant cells were encountered in the follicles of the spleen and in the lymph nodes of a large proportion of the animals receiving the antigen. Similar granulomas in the spleen and lymph nodes as well as in other tissues have been described in polyarteritis nodosa. The present experimental demonstration that an epithelioid and giant cell reaction may result from hypersensitivity provides evidence for the allergic origin of those cases of polyarteritis nodosa of unknown etiology containing this type of lesion. In the present study the time of development of the cardiovascular, renal, and granulomatous lesions was determined in relation to the blood clearance of antigen and the time of appearance of circulating antibody. All the tissue lesions developed during the "immune" phase of antigen elimination and regressed after the antigen had been completely eliminated and free antibody had appeared in the circulation. These temporal relationships indicate that the tissue lesions which occur after the intravenous administration of foreign protein are the result of antigen-antibody combination.

Total serum hemolytic complement activity is consistently reduced in animals undergoing accelerated "serum sickness". The time of maximum reduction in complement titer invariably coincides with the time of complete antigen disappearance. This temporal relationship supports the belief that the reduction in complement titer is brought about by in vivo antigen-antibody combination. The intravenous administration of a single daily large dose of BGG-precipitated complexes produces a marked but temporary reduction in total complement hemolytic activity. On the other hand, multiple injections of soluble BGG immune complexes prepared in antigen excess failed to even temporarily alter complement titers. Animals undergoing the development of accelerated "serum sickness" treated by either type immune complex showed a significantly reduced incidence of arterial lesions. Apparently, this inhibiting effect on the development of arterial lesions was independent of variations in total complement hemolytic activity.

Cortisone markedly suppressed the cardiovascular and renal lesions of serum sickness type hypersensitivity which ordinarily develop following the intravenous injection of bovine albumin. The inhibitory effect of cortisone on the allergic granulomatous lesions of the spleen was less striking; the lesions were less extensive, but the percentage of animals affected was unchanged. Cortisone in the dosage employed had no effect on the elimination of antigen following its intravenous administration or on the appearance of circulating antibody. These findings indicate that inhibition of the lesions of serum sickness by cortisone does not depend on the suppression of antibody production. Therefore, it is inferred that cortisone somehow protects the animal from the damaging effects of antigen-antibody union.