Studies of the acute phase response in experimental serum sickness

The acute phase behavior of C-reactive protein (C-RP), the third component of complement (C3) and total haemolytic complement activity was studied during the course of acute serum sickness (ASS) in rabbits. The specific aim was to establish whether the induction protocol caused a significant change in the serum concentration of proteins (such as C3) which could modify the outcome of the disease. ASS was induced by an intravenous (IV) bolus of bovine serum albumin (250 mg/Kg) with or without prior subcutaneous (SC) immunization with 4 mg BSA in complete Freund's adjuvant. Thirty-six animals received a full induction regimen (i.e., both SC and IV BSA). A further six rabbits were given either IV or SC BSA alone, in order to define the basis for acute phase changes observed when both injections were given. Twelve animals received a standard acute phase stimulus with intramuscular (IM) turpentine--2 or 3 ml--as a comparison to the response observed in the experimental animals. Nine, 14 and 24 animals showed a rise in C-RP (i.e., five-fold increase), C3 and haemolytic activity (greater than 25% increase) respectively after a full induction protocol. Eight, nine and five animals showed a comparable rise with IM turpentine. Studies with IV or SC BSA alone showed that the latter was predominantly responsible for the rise in C-RP and haemolytic activity. Specifically, five and four animals respectively showed a significant rise in these two parameters. Three animals showed a rise in C-RP following IV BSA alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of progressive glomerulosclerosis in experimental chronic serum sickness

A rat model of chronic serum sickness was used to study the pathogenesis of progressive glomerulosclerosis complicating experimental immune-complex glomerulonephritis. Chronic serum sickness was induced by immunising rats with bovine serum albumin followed by intraperitoneal administration of the antigen. Early lesions consisted of mesangial deposits of rat immunoglobulins, followed later by transient subendothelial and persistent subepithelial immune aggregates. On the basis of the peak level of proteinuria around day 80, three groups of rats were distinguished: I physiological proteinuria; II 50-500 mg/24 h; and III greater than 500 mg/24 h. The animals were killed at day 220 and the presence of mesangial proliferation, epithelial proliferation, and synechiae, as well as focal glomerulosclerosis was scored. It appeared that all and only proteinuric animals developed progressive glomerulosclerosis, although all three groups of animals passed through a phase with mesangial and subendothelial immune deposits. A strong correlation was found between the degree of proteinuria and the proportion of glomeruli affected. We conclude that the combination of mesangial and subendothelial deposits on the one hand and subepithelial deposits associated with increased protein loss on the other constitute a conditio sine qua non for the development of progressive glomerulosclerosis in this model. The use of specific antibodies to investigate the composition of the sclerotic lesions showed the presence of laminin and type IV collagen, but not of types I and III collagen in sclerotic areas of glomeruli. This indicates that the development of progressive glomerulosclerosis in this model is due to an increased production of glomerular basement membrane components by presumably solely glomerular cells after the occurrence of immunological glomerular injury.

Sudden onset of proteinuria in chronic serum sickness in rats

1. Daily intravenous administration of bovine serum albumin (BSA) to rats produces chronic serum sickness glomerulonephritis, an immune-complex-mediated renal disease that is eventually always fatal. We have performed a detailed study of the onset of proteinuria in chronic serum sickness in order to assess the long-term consequences of discontinuing daily BSA injections precisely at that very early and well-defined stage of disease. 2. Urine and plasma samples from rats receiving daily BSA injections were collected and analysed daily before the onset of proteinuria, at which time the rats were divided into three groups. Group 1 continued to receive daily BSA injections, in group 2 injections were stopped on the first, and in group 3 on the third, day of proteinuria. Proteinuria began suddenly and was not preceded either by microalbuminuria or abnormalities of plasma composition. The sudden expression of proteinuria was accompanied by an equally rapid development of hypoalbuminaemia and hypercholesterolaemia. Development of the characteristic glomerular histopathology of serum sickness coincided with, but did not precede, the onset of proteinuria. Despite the discontinuation of antigen injections at the onset of proteinuria, basement membrane thickening was evident 8 weeks later; proteinuria persisted and hypercholesterolaemia increased. 3. In this model of immune complex glomerulonephritis, changes in kidney function and immunopathology were abrupt and closely linked, precluding the use of those criteria to predict when proteinuria would begin. Furthermore, extremely brief periods of active immunological injury to the peripheral capillary wall were sufficient to produce persistent abnormalities of glomerular structure and function.

Glomerular eicosanoid production in acute serum sickness nephritis

To determine if the induction of immune-mediated glomerular injury influences the formation of glomerular cyclooxygenase products, we measured thromboxane B2 (TXB2), 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and prostaglandin E2 (PGE2) production by isolated glomeruli of rabbits induced with acute serum sickness nephritis by the administration of bovine serum ablumin (BSA). Animals were randomly assigned to one of three experimental groups: animals injected with BSA (BSA group; n = 11); animals injected with normal saline (control group; n = 11); and animals injected with BSA which were treated with the thromboxane synthetase inhibitor, OKY-046 (BSA + OKY-046; n = 6). Animals in the BSA and BSA + OKY groups developed severe proteinuria and glomerular histologic lesions of nephritis. No differences in proteinuria, serum creatinine and severity of histologic nephritis were observed between the two groups. Examination of glomerular eicosanoid production at the end of the experiment showed a marked reduction of glomerular PGE2 and 6-keto-PGF1 alpha production with a smaller reduction of glomerular TXB2 production in the BSA group. In the BSA + OKY-046 group, the production of TXB2 was significantly less than that in the BSA group; despite this, no effect on proteinuria could be discerned.

Bovine serum albumin (BSA) nephritis in rats. VII. In vivo kinetics of polymorphonuclear leukocytes

In vivo quantitation of polymorphonuclear leukocytes (PMN) was carried out and their accumulation kinetics were determined by adoptive transfer of 51Cr-PMN in control rats, nephritic but non-proteinuric rats and nephritic rats with heavy proteinuria. Nephritis was induced by daily administration of antigen to preimmunized rats for 4 weeks. Renal accumulation of 51Cr-PMN was maximal at 3 h after the adoptive transfer in diseased rats, to which the last antigen administration was given 24 h prior to the kinetic study. Histologically, however, a considerable number of PMN had infiltrated into the glomeruli of these rats at any given time during the 24-h period, i.e., the time interval between antigen challenges. Two pieces of evidence strongly suggest that circulating PMN adhere to glomeruli, stay there for a short time and then become dispersed again into the circulation. When antigen was administered after 51Cr-PMN transfer, the PMN disappeared promptly from the circulation and accumulated in the lungs and liver, resulting in a lack of any peak in the kidney PMN kinetics. It is concluded that the presence of an appreciable number of PMN in the glomeruli reflected the dynamic balance of cell influx and efflux.

Chronic serum sickness glomerulonephritis: modification of the immune response influences the rate of removal of mesangial electron-dense deposits

We have used a chronic serum sickness model of glomerulonephritis to investigate whether gross interference with the immune system can influence the rate of removal of antigen and established electron-dense deposits from the glomerulus. Radio-labelled cationized bovine serum albumin (BSA) was used as antigen. During the 2 weeks after the cessation of injections, the rate of removal of antigen from isolated glomeruli and from renal cortex, liver, spleen, and lung was measured. The rate of removal of mesangial and subepithelial deposits was assessed by point-counting. Urinary excretion of free and protein-bound isotope was also measured. Having quantified the rate of removal of antigen and deposits from the glomerulus, we attempted to influence the rate of removal by interfering with the immune response in the course of recovery. Contrary to our expectations, stimulation of the immune system with antigen in Freund's complete adjuvant, 4 days after the last injection of antigen, inhibited the removal of antigen and mesangial electron-dense deposits. Prednisolone had no detectable effect, but large doses of a non-nephritogenic form of the antigen (native BSA) enhanced removal. Removal of antigen and mesangial deposits was inversely correlated with the levels of circulating anti-BSA antibody, suggesting that specific antibody, circulating through the mesangium, inhibits the removal of antigen which is already trapped at that site. None of the forms of intervention applied during recovery produced a detectable change in the rate of removal of subepithelial deposits.

Human serum sickness: a prospective analysis of 35 patients treated with equine anti-thymocyte globulin for bone marrow failure

We have prospectively evaluated the clinical and immunological features of serum sickness in 35 patients treated for bone marrow failure with anti-thymocyte globulin (ATG 15 mg/kg/day) and methylprednisolone (1 to 1.5 mg/kg/day). Twenty-one patients were treated for 10 days and 14 were treated for 28 days. Clinical evidence of serum sickness developed in 30 patients (86%) and included fever and malaise (100%), cutaneous eruptions (93%), arthralgias (67%), gastrointestinal complaints (67%), cephalgia (57%), blurring of vision (37%), arthritis, (30%) and lymphadenopathy (13%). Clinical serum sickness began on day 7 +/- 1 (X +/- S.E.M.) and lasted for 10 +/- 2 days in the 18 affected patients receiving the shorter course of ATG. In the 12 affected patients receiving the longer course of ATG, serum sickness began on day 9 +/- 1. The earliest manifestations of serum sickness were fever, malaise, and cutaneous eruptions. Cutaneous findings consisted of morbilliform eruptions (n = 19) and urticaria (n = 1) or a combination (n = 8) that lasted 10 to 14 days. Twenty-one patients (75%) developed a highly characteristic serpiginous band of erythema and purpura along the sides of the fingers, toes, palms and soles 12 to 48 hours before other symptoms of serum sickness. Biopsies of lesional skin during the course of serum sickness revealed immune deposits (IgM, IgE, IgA and C3) in dermal vasculature in 7 of 9 patients. Immunological changes that occurred during the course of serum sickness included increased serum levels of IgG, IgM, IgA, and IgE. Circulating immune complexes, as measured by the C1q-binding assay, increased from a mean value of 12% to 45% on day 13 +/- 1. Complement levels (C3, C4, and CH50) decreased 50 to 80% from their baseline levels on day 10 +/- 2. Acute phase reactants increased: erythrocyte sedimentation rate, C-reactive protein and beta-2 microglobulin. Abnormal urinalysis developed in 17 patients (57%) over the course of serum sickness and included proteinuria, hematuria and hemoglobinuria on day 10 +/- 3. Hematopoietic response occurred in 43%. All 5 patients who did not develop serum sickness recovered from bone marrow failure. Our data document the clinical and immunopathological findings in human serum sickness and suggest that the principles of antigen-antibody interaction, complement activation, and resultant inflammatory response as seen in the previous animal studies are directly applicable to studies of patients with serum sickness.

An experimental study of atherosclerosis as a sequela of coronary arteritis

In order to examine the effect of corticosteroids on coronary atherogenesis in collagen diseases, an experimental study of serum sickness was performed. Forty-two rabbits were divided into four groups (Groups A-D). Group B, C and D rabbits received four intravenous injections of bovine serum albumin (250 mg/Kg) at 16-day intervals. Groups A, C and D rabbits were fed ad libitum cholesterol supplemented diet (1%) 16 days after the last injection. Group D rabbits received subdermal injections of prednisolone (1 mg/Kg) three times per week in the same period. After 124 days, all rabbits were sacrificed. Serum cholesterol and phospholipid increased in Group A, C and D rabbits. Group A rabbits showed intimal foam cell proliferation. Group B rabbits showed slight fibrous intimal thickening. The coronary arteries of Group C rabbits showed fatty-proliferative intimal thickening and an increase in the incidence of vascular lesions (13.9% of the coronary arteries as compared with 11.7% for Group A and 8.4% for Group B). The coronary lesions of Group D showed the same pattern as those of Group C, but the incidence of lesions was 6.0%. It was concluded that prednisolone did not augment immunologically induced atherosclerosis.

Antinephritic effect of prostaglandin E1 on serum sickness nephritis in rats (4). Enhanced clearance of macromolecules by the reticulo-endothelial system with prostaglandin E1

Function of the reticulo-endothelial system (RES) was determined by the carbon clearance technique in rats. Rats in the previous phase of nephritis showed reduced function of the RES with circulating immune complexes compared with normal rats. Prostaglandin E1 (PGE1) at 1.0 mg/kg, s.c., resulted in significant recovery in the impaired RES activity of the rats in the previous state of nephritis. Dipyridamole, 400 mg/kg, p.o., slightly enhanced function of the RES, but 20 mg/kg azathioprine, p.o., did not. Thus, the enhanced RES activity with PGE1 can explain part of the antinephritic effect of PGE1.

Serum sickness nephropathy in the rat using cationized albumin: effect of preimmunization and antigen dose

A model of glomerulonephritis induced in preimmunized rats with cationic albumin is described. Extensive glomerular immune complex formation and a severe nephrotic syndrome occurred within 5 days of commencement of daily intravenous injections. Severity of disease was markedly influenced by the degree of preimmunization and, to a lesser extent, by the dose of cationic albumin administered. Immune deposits, although initially confined along the capillary loops, were seen at all sites in the glomerulus. This study confirms that, in rats, the use of cationic antigens accelerates the development of 'serum sickness' nephropathy but preimmunization is necessary to produce significant disease.

Serum-sickness-like disease is a common cause of acute arthritis in children

Among 283 children in a prospective study of arthritis we found 15 patients with a self-limited serum-sickness-like disease consisting of urticaria or joint erythema and mostly polyarticular arthritis. The mean duration of joint symptoms was 5.9 days. A preceding infection was reported in 12 patients and 12 had received drugs, the therapy starting on average 12.8 days before the onset of joint symptoms. In 9 cases the drug was penicillin. Four patients had recurrent attacks. Circulating immune complexes were detected in the serum of 12 patients, but specific IgE antibodies to penicillin only in 3 patients. The estimated annual incidence of the condition was 4.7/100,000 children under age 16.

Identification and quantitation of cells that process immune complexes in nephritic rats induced with bovine serum albumin

A light microscopic autoradiography was used to determine which cell types positively disposed of the daily circulating immune complexes produced in rats with experimental immune complex glomerulonephritis. Our results indicated that polymorphonuclear leucocytes (PMNs) remove large quantities of immune complexes in the livers, spleens, and lungs of these rats. Semiquantitative autoradiography indicated further that the function of mononuclear phagocyte system decreased late in the course of glomerulonephritis; whereas, in compensation, the role of PMNs appeared to increase. Our data uncovered a significant role for PMNs in the disposition of immune complexes during the induction of experimental immune complex nephritis.

Antinephritic effect of prostaglandin E1 on serum sickness nephritis in rats. (3). Suppression of leukocytes by prostaglandin E1 as a mechanism for preventing immune complex glomerulonephritis

Serum sickness nephritis was produced in rats by repeated i.v. injections of rabbit serum albumin. After 12 weeks of antigen injection, the rats with proteinuria were subjected to a renal biopsy. Then half of the group was continuously given 300 micrograms/rat/day of PGE1 . alpha-cyclodextrin (PGE1 . CD) with mini osmotic pumps for 3 weeks. PGE1 . CD inhibited the development of glomerulonephritis and the deposition of immune complexes in the glomeruli, although the control group showed developed glomerular alteration and increased immune deposits in the glomeruli in the autopsy specimens. PGE1 . CD particularly improved the intraluminal hypercellularity of the histological findings. In the early stage of this model, 0.5 and 1.0 mg/kg of PGE1 and 6.0, 12.5 and 25.0 mg/kg of azathioprine were administered s.c. and p.o., respectively, for 3 weeks. There was a significant suppression of about 20% in the 1.0 mg/kg PGE1 group on the antibody synthesis as compared with the control group throughout the experimental period, although the inhibition was less than that of azathioprine. In the same experimental protocol, PGE1 significantly suppressed the increase in leukocyte counts; at the third week after PGE1, the number of leukocytes was 25.6 +/- 4.2 X 10(3) in the control group and and 14.1 +/- 3.0 X 10(3) in the 1.0 mg/kg PGE1 group. It is considered that PGE1 could excert the antinephritic effect in this mode through decreasing the leukocyte counts in the circulation and the glomeruli independently of immune deposits in the glomeruli.

Disorders that mimic CNS infections

A variety of inflammatory and neoplastic disorders can cause signs, symptoms, and laboratory abnormalities suggesting CNS infection. The distinction usually can be made through careful consideration of the entire clinical picture and the judicious use of additional laboratory tests.

Drug-associated glomerulopathies

The renal glomeruli are vulnerable to injury by a number of drugs and other toxic agents. These agents may lead to damage by one of two basic mechanisms: direct, dose-related toxic injury; indirect, immunologically mediated injury, largely dose-independent. Proteinuria is the simplest and most important functional indicator of glomerular injury. It occurs almost immediately in direct toxic injury, but there is a latent period of weeks to months with immunologically mediated processes. Of the two mechanisms, the second is by far the more common in clinical settings. The best studied experimental agent causing direct toxic injury is the aminonucleoside of puromycin. Clinically, perhaps the most important agent is Cyclosporine A. Although this agent is usually thought of primarily as a tubular toxin, it is capable of giving rise to a microangiopathic glomerular lesion similar to that in the hemolytic uremic syndrome. The classic model for immunologic glomerular lesion is Heymann nephritis, which produces a membranous glomerulopathy. Clinically, most drug mediated glomerulopathies also take the form of a membranous nephropathy, usually with a frank nephrotic syndrome. Among the more common offenders are penicillamine, gold salts used in rheumatoid arthritis, and captopril used in hypertension. The other common type of drug-related glomerulopathy occurs as part of a lupus-like syndrome induced by a variety of drugs, including hydralazine, procainamide, and penicillamine. All of these give rise to a variety of antibodies, most prominently antinuclear antibodies, and in the more severe cases there may be lupus-like glomerular lesions as well.

Glomerular arachidonate lipoxygenation in rat nephrotoxic serum nephritis

Arachidonate lipoxygenation to monohydroxylated eicosatetraenoic acids (HETE) was studied in rat nephrotoxic serum nephritis (NSN). A single infusion of nephrotoxic serum enhanced conversion of [3H]arachidonic acid ([3H]C20:4) to [3H]12-HETE in glomeruli isolated from nephritic rats compared with controls. The percent conversion of [3H]arachidonic acid was 1.95 +/- 0.2% in control glomeruli and 14.2 +/- 2% in nephritic glomeruli 2 d after induction of disease. No significant changes in the conversion of [3H]C20:4 to [3H]5-, 8-, and 9-HETE were noted. Extraction of glomerular HETE by alkaline hydrolysis, to evaluate possible reacylation of HETE after their production, confirmed the presence of 12-HETE and did not provide evidence of 5-HETE synthesis. Increased glomerular 12-HETE synthesis in nephritic rats was also demonstrated by high pressure liquid chromatography-UV detection and by 12-HETE radioimmunoassay. The enhanced glomerular 12-HETE synthesis commenced as early as 3-5 h after administration of nephrotoxic serum and peaked at day 2 with 10-fold enhancement of 12-HETE production. Increments of glomerular 12-HETE persisted on day 7 and returned toward control levels by day 14. Platelet depletion, induced by antiplatelet antisera, did not decrease glomerular 12-HETE synthesis in NSN, thereby eliminating platelets as the cellular origin of 12-HETE. Glomerular epithelial and mesangial cells are the most likely sources of enhanced 12-lipoxygenase activity. The enhanced arachidonate 12-lipoxygenation in glomerular immune injury could have important proinflammatory effects in the evolution of glomerulonephritis since 12-HETE has important effects on leukocyte function.

Macrophage-induced glomerular fibrin deposition in experimental glomerulonephritis in the rabbit

Glomerular fibrin deposition is important in the pathogenesis of renal failure and crescent formation in glomerulonephritis. The mechanisms of glomerular fibrin deposition are unknown. The current studies explored the role of macrophages in this process. Methods were developed for measuring glomerular fibrin deposition and glomerular procoagulant activity in a passive model of the autologous phase of antiglomerular basement membrane antibody-induced glomerulonephritis in rabbits. Significant fibrin deposition was observed to be associated with glomerular macrophage accumulation. Leukocyte ablation with mustine hydrochloride prevented both glomerular macrophage accumulation and fibrin deposition without affecting the coagulation system or the deposition of disease-inducing antibodies and complement. Repletion with mononuclear inflammatory cells produced significant fibrin deposition. To examine the role of tissue injury per se in glomerular fibrin deposition, a macrophage-independent model of glomerular injury (heterologous phase glomerulonephritis) was also studied. Although a similar degree of glomerular injury occurred, there was no significant fibrin deposition. This suggests that macrophages, rather than injury alone, are responsible for fibrin deposition. Lysates of isolated glomeruli containing macrophages demonstrated greatly enhanced procoagulant activity compared with lysates of glomeruli without macrophages. Thus macrophages appear to be directly responsible for glomerular fibrin deposition in antiglomerular basement membrane antibody-induced glomerulonephritis, and this appears to be due to their ability to express procoagulant activity rather than their propensity to cause glomerular injury.

Cutaneous manifestations of serum sickness in patients receiving antithymocyte globulin

We have prospectively evaluated the cutaneous manifestations of serum sickness in thirty-five patients treated with horse antithymocyte globulin for bone marrow failure. Twenty-one patients (21/35) were treated with antithymocyte globulin (15 mg/kg/day) for 10 days, and fourteen of thirty-five patients were treated with antithymocyte globulin (15 mg/kg/day) for 14 days and then every other day for an additional 14 days. Clinical evidence of serum sickness developed in thirty patients and included fever and malaise (100%), cutaneous eruptions (93%), arthralgias and myalgias (67%), gastrointestinal complaints (67%), and lymphadenopathy (13%). Cutaneous findings consisted of morbilliform eruptions (n = 19), urticaria (n = 1), or a combination of these two reaction patterns (n = 8). Cutaneous manifestations of serum sickness began on day 7 +/- 1 and lasted for 12 +/- 2 days for the group as a whole. Biopsies of lesional skin revealed mild perivascular lymphohistiocytic infiltrates by light microscopy in these leukopenic patients. Direct immunofluorescence microscopy of lesional skin from patients with serum sickness demonstrated immunoreactants in seven of nine subjects (78%). Immunoreactants were confined to the walls of dermal blood vessels and consisted of IgM (7/9), C3 (6/9), IgE (5/9), and IgA (4/9). IgG (horse or human) was not identified in any of these specimens. Twenty-one patients (21/28) also developed an erythematous eruption on the sides of the fingers, toes, palms, and soles 12 to 48 hours prior to their morbilliform eruption. This study describes the cutaneous manifestations of human serum sickness occurring during therapy with horse antithymocyte globulin, documents a cutaneous sign of serum sickness, and suggests that the cutaneous eruptions associated with human serum sickness are immunologically mediated.

The mechanism of action of corticosteroids on glomerular injury in acute serum sickness in rabbits

Macrophages have recently been identified as the predominant mediators of the glomerular injury in acute serum sickness (AcSS) in rabbits. Corticosteroids have been shown to prevent this lesion, but the mechanism of this effect is unknown. As corticosteroids are potent anti-macrophage agents, the effect of prednisolone treatment (2 mg/kg/day) on glomerular macrophage accumulation and injury was assessed in rabbits developing AcSS. Eleven untreated animals all developed a proliferative endocapillary glomerulonephritis (mean 71.7 +/- 1.9 sem cells per glomerular cross section, c/gcs) with glomerular macrophage accumulation (46.3 +/- 5.7 macrophages per glomerulus, macs/glom) and proteinuria (555 +/- 379 mg/24 h). Eight animals were treated with prednisolone commencing not more than 48 h prior to immune elimination (IE). Glomerular injury was markedly attenuated with significantly less cellular proliferation (49.1 +/- 2.1 c/gcs, P less than .005), fewer macrophages within glomeruli (10.5 +/- 7.7 macs/glom, P less than .005) and minimal proteinuria (19.3 +/- 5.5 mg/24 h, P less than 0.01). Treatment did not alter the amount of circulating BSA-anti-BSA immune complex; its time of IE (11.1 +/- 0.4 days treated, 11.4 +/- 0.4 days untreated) its renal deposition (2.36 +/- 0.64 micrograms BSA/g renal cortex treated, 2.66 +/- 0.52 mg BSA/g renal cortex untreated) or its glomerular localization. These results indicate that prednisolone treatment can effectively reduce the glomerular injury of AcSS. This effect is not dependent on any alteration of immune complex formation or deposition, but involves reduction of macrophage accumulation at the inflammatory site.

An experimental model of nephritis induced by calf serum injection in mice

Acute glomerulonephritis characterized by proteinuria, hypoalbuminemia and leukocytosis was induced in mice by repeated intraperitoneal injections of calf serum (1 ml/mouse X 10). In mice treated with calf serum, hypercellularity, karyorrhexis, expansion of the mesangium and hyalinosis in the glomeruli were observed by light microscopy. Furthermore, circulating immune complexes were detected in the serum, and deposits of mouse IgG and C3 on the basement membranes of the glomeruli were demonstrated immunohistochemically. Oral administration of cyclophosphamide or 6-mercaptopurine at a dose of 20 mg/kg/day significantly suppressed the development of this nephritis. Dexamethasone (0.5 mg/kg/day) caused moderate inhibition of the nephritic changes. These results suggest that this experimental model may be useful for evaluation of anti-nephritic drugs.

Splenomegaly and immune complex splenitis in rabbits with experimentally induced chronic serum sickness: immunopathological findings

This study describes the morphological and immunocytochemical aspects of the spleen in rabbits with experimentally induced chronic serum sickness. Thirty-seven rabbits were immunized with daily injections of bovine serum albumin (BSA) and six served as non-immunized controls. The most significant lesions were found in rabbits with chronic serum sickness induced by high doses of BSA. The spleens were increased in size and in weight. Granular deposits of BSA, rabbit IgG and C3, presumably immune complexes (IC), were found in the basement membranes of the venous sinuses and of the capillaries in the marginal zone, in the walls of splenic arterioles and, occasionally, between the macrophages in the splenic cords and lymphoid cells in lymphatic follicles. An increased number of degranulated polymorphonuclear leukocytes, macrophages and giant cells, degenerative changes of dendritic cells and, in some instances, splenic fibrosis were also seen. These splenic lesions developed when the concentration of BSA-antibodies in the sera decreased. The spleens of rabbits receiving high doses of BSA in a stage between acute and chronic serum sickness were also increased in size and in weight. The red pulp was enlarged, and immune deposits were observed within macrophages but not in splenic structures. The spleens of non-responder rabbits had a slight decrease in number of lymphatic follicles and germinal centers only. The spleens of non-immunized rabbits were consistently normal. The results indicate that in rabbits receiving multiple injections of high doses of BSA, chronic serum sickness is associated with splenomegaly and IC-splenitis and that these lesions occur when the level of circulating BSA antibody declines. IC-splenitis could impair the clearance of IC and influence the immune function of the spleen. These findings could have implications in the pathogenesis of splenomegaly and of defective splenic function in human IC-mediated diseases.