Mechanisms in the suppression of delayed hypersensitivity in the guinea pig by 6-mercaptopurine

Peripheral ulcerative keratitis in the setting of rheumatoid arthritis: treatment with immunosuppressive therapy

Peripheral ulcerative keratitis (PUK) is a rare but serious inflammatory eye condition that can complicate rheumatoid arthritis. PUK can be a warning sign of impending vasculitis, and cytotoxic therapy may be necessary to induce remission. We have encountered three patients with PUK in the past year. Two patients had long-standing quiescent rheumatoid arthritis who developed photophobia. Diagnosis was made by slit lamp examination. Treatment with local cyclophosphamide and prednisone resulted in prompt remission of the ulcer within 8 weeks. Cytotoxic therapy was discontinued altogether within 6 months. The third patient was also treated successfully with oral steroids and azathioprine. In all patients, sicca was noted. None of them had any evidence of systemic vasculitis. PUK, when recognized early and treated aggressively, can result in remission of the ulcer and in the prevention of vasculitis. Keratoconjunctivitis sicca can accompany PUK independent of the activity of rheumatoid arthritis.

Effect of salai guggal ex-Boswellia serrata on cellular and humoral immune responses and leucocyte migration

Effect of alcoholic extract of salai guggal (AESG) was studied on cellular and humoral immune responses in mice and leucocyte migration in rats. Oral administration of AESG strongly inhibited the antibody production and cellular responses to sheep red blood cells in mice. It inhibited the infiltration of polymorphonuclear leucocytes and reduced the volume of pleural exudate in carrageenan induced pleurisy in rats. It showed no cytotoxic effect.

Drug influences on rat hepatic macrophage enzyme production and release in vitro

Drug influences on hepatic macrophage enzyme release have been investigated using a rat model of macrophage recruitment and activation. N-acetyl-glucosaminidase (NAG), a lysosomal enzyme, and plasminogen activator (PA), a cytosolic enzyme, have been measured in both cell lysates and supernatants after 24 h in culture. 6-mercaptopurine (6-MP) and azathioprine significantly decreased (P less than 0.03) the enhanced production of NAG by recruited macrophages following stimulation in vitro (total NAG activity, nmol substrate hydrolysed/microgram cell protein; recruited macrophages exposed to endotoxin, no drug exposure 0.63 +/- 0.08, azathioprine 0.44 +/- 0.08, 6MP 0.36 +/- 0.06). Prednisolone, azathioprine and 6MP significantly reduced (P less than 0.05) the supernatant release of PA in response to endotoxin exposure in vitro by both cell types (supernatant PA values after 24 h in culture, recruited macrophages exposed to endotoxin, no drug 26.0 +/- 2.9 units, prednisolone 18.5 +/- 1.7 units, levamisole 27.3 +/- 4.7 units, azathioprine 18.1 +/- 2.3 units, 6MP 17.3 +/- 1.5 units). The results from this study indicate that certain drugs used in human liver disease are able to modify the secretory activity of rat hepatic macrophages.

The influence of cyclophosphamide and 6-mercaptopurine on the IgG1 and IgG2 immune response in guinea-pigs

The purpose of this study was to investigate the effect of cyclophosphamide (CY) and 6-mercaptopurine (6-MP) on the production of the two IgG antibody subclasses in guinea-pigs. Following the intradermal application of dinitrophenylated bovine gamma globulin (DNP20-BGG) emulsified in Freund's incomplete adjuvant (FIA) each animal was given CY or 6-MP, 10 mg per kg of body weight per day on days 1--7, and the DNP- and BGG-specific anaphylactic (IgG1) and lytic (IgG2) antibodies were determined. Only treatment with CY resulted in a significantly-depressed IgG2 anti-DNP immune response; 6-MP was not suppressive and caused a prolonged IgG2 anti-DNP production. Both substances showed a stimulatory effect on IgG1 anti-DNP antibody formation. The carrier-specific IgG1 and IgG2 antibody levels were suppressed completely by CY but unaffected by 6-MP. After a booster injection of 1 mg BGG on day 86 the animals in the CY-treated group were not able to mount a secondary IgG2 anti-BGG immune response. In contrast, IgG1 anti-BGG production was strong and uninfluenced by CY treatment.

Mechanisms in the suppression of delayed hypersensitivity in the guinea pig by 6-mercaptopurine. II: Kinetic and morphologic studies on the monocyte-macrophage component

The effect of 6-mercaptopurine on the development and expression of delayed hypersensitivity was studied in the guinea pig. Results indicated that 6-MP produced its suppressive effects primarily by action on cells of the monocyte-macrophage series. Suppression could occur under conditions of both developing and pre-established delayed hypersensitivity. The defect primarily involved newly synthesized, bone marrow-derived monocytes. Marked alterations in monocyte macrophage generation and distribution, especially the T1/2 of circulating monocytes were demonstrated. Suppressive effects were associated with the appearance of a unique morphologic microscopy. Finally, the in vivo expression of delayed hypersensitivity correlated better with a variety of parameters relating to qualitative macrophage function and distribution rather than those relating to quantitative macrophage levels.

The effects of azathioprine and 6 MP on immunity

The thiopurines, azathioprine and 6 MP are potent inhibitors of both experimental and clinical immune responses. The primary pharmacological activities are mediated by competitive inhibition of enzymes concerned with de novo purine base synthesis; Immunosuppressive activities appear to result from cytotoxic activities directed against antigen-responsive lymphocytes; this inhibition is maximal when the treatment course coincides with the proliferative expansion phase of the response. By contrast, thiopurines are comparatively ineffective if used during an effector phase of an immune response. Furthermore, administration prior to antigenic challenge does not lead to immune inhibition; in fact, it may lead to augmentation of selected immune responses. Treatment with thiopurines does not result in acute lymphopenia; prolonged courses will cause a moderate decrease in circulating lymphocytes. The drug does not selectively deplete peripheral T or B cells but can acutely reduce K (killer) cells, which are effectors in ADCC responses. In addition, short-lived thymocytes and marrow lymphocytes are rapidly depleted by these anti-metabolites. Many in vitro functions of lymphocytes, from treated animals remain normal. Recent studies indicate that, in vitro, azathioprine is specifically able to bind murine T lymphocytes; this can be shown by their ability to inhibit their capacity to rosette with sheep erythrocytes. Azathioprine is also a potent inhibitor of mixed lymphocyte culture responses and can readily suppress the in vitro generation of cytotoxic T cells. These observations suggest that drugs exert preferential toxicities for murine T cells. B lymphocytes for mice appear to vary in their susceptibility for thiopurines. By contrast, the activity of human B cells can be readily suppressed with this drug whereas T helper function is comparatively resistant. In addition to immunosuppressive properties, thiopurines are capable of exerting anti-inflammatory activities, primarily by inhibiting the replication of hematopoietic precursors.

Effect of nonsteroidal anti-inflammatory and other pharmacological agents on tuberculin reaction

Nonsteroidal anti-inflammatory and other pharmacological agents were tested in the efferent arc of the tuberculin skin reaction in the guinea pig. A low but significant inhibition was produced by the acidic anti-inflammatory agents, including the arylalkanoic acids, the anthranilic acids, indomethacin, and phenylbutazone. Some nonacidic anti-inflammatory agents also were inhibitory; benzydamine caused a high inhibition. Except for methotrexate, the antineoplastic--antimetabolite agents were not potent inhibitors. Inhibition without toxicity was produced by the coumarin anticoagulants, the diuretics, chloroquine, tilorone, and the following immunoregulators: antithymocyte gamma-globulin, cyclophosphamide, and penicillamine. Levamisole, colchicine, heparin, and niridazole were inhibitory but produced lethality either at or above the effective dose.

The effect of azathioprine on cell-mediated immunity (CMI) to Candida albicans in Crohn's disease

Using as antigen a suspension of Candida albicans, strain A, three tests of cell-mediated immune reactivity (delayed skin hypersensitivity, lymphocyte stimulation and leucocyte migration inhibition) were undertaken in patients with Crohn's disease to determine the effect of azathioprine given as the sole anti-inflammatory medication. No significant effect was demonstrable on 48 hr induration in the skin test. Uptake of thymidine by lymphocytes in vitro, whether spontaneous or antigenically induced, was greater during azathioprine treatment than before it. The assumption that this finding might be associated with clinical recovery was confirmed in antigen-stimulated cultures by the fact that, irrespective of treatment, patients who had been able to resume their normal occupations showed markedly higher reactivity than those who were still disabled (P<0·002). It was also found that azathioprine treatment in itself potentiated lymphocyte stimulation by C. albicans. The range of values for inhibition of leucocyte migration was the same in the treated and untreated groups, but certain individuals displayed a substantial change in reactivity when re-tested after institution or discontinuation of azathioprine treatment. Untreated patients with Crohn's disease did not differ from normal subjects in their cell-mediated reactivity to C. albicans. The increased rate of thymidine uptake by lymphocytes from patients receiving azathioprine is discussed in the light of recent hypotheses linking virus-induced malignancy with lymphoblastic transformation.

Activity of various immunosuppressive drugs on tuberculin hypersensitivity reaction in chickens

Drug induced immunosuppression of chicken immune response was studied in F1 hybrids of the CB and IC inbred lines. In tuberculin reaction complete inhibition of wattle swelling was induced by the administration of methotrexate, colcemid (1 mg/KBW), and 6-mercaptopurine. The cellular infiltration was substantially reduced in these cases. Cyclophosphamide and colcemid (0.1 mg/KBW) reduced partially the wattle swelling but had no apparent effect on the cellular infiltration. Acetinomycin D did not affect in measurable degree the wattle swelling. The histologic picture was in this case the same as in the control animals. The same drug administration schedule had less pronounced effect on anti-HSA antibody production. No anti-HSA antibody was found after the 500 mg/animal doses of 6-mercaptopurine. Significant reduction of anti-HSA titres was found after 50 mg/animal doses of 6-mercaptopurine, colcemid (1 mg/KBW), 25 MG/KBW or cyclophosphamide and after the methotrexate treatment.

Mechanisms of specific and non-specific tumour immunity after azathioprine treatment of mice

The ability of phagocyte-depleted spleen cells to lyse chicken erythrocytes (CRBC) in the presence of antibody was measured in mice which had been treated with the antimetabolite azathioprine. Single doses of the drug had no effect on this ability when measured on the day after administration. A 4-day course of 80 mg/kg/day of the drug markedly reduced splenic antibody-dependent cell-mediated cytotoxicity (ADCMC) although it reduced neither antibody responses nor the development of cytotoxic cells following subsequent immunization with an allogeneic tumour. Splenic phagocytosis and phagocyte-mediated ADCMC were both slightly enhanced following drug treatment. The implications of these findings are that the major antibody-dependent cytotoxic cell in phagocyte-depleted mouse spleen is normally in a state of proliferation, and plays no important role in antigen recognition.

Substituted 9-benzyladenines: inhibitors of inflammation associated with the delayed hypersensitivity skin reaction

Members of a group of substituted 9-benzyladenines have been identified as effective inhibitors of inflammatory aspects of the delayed hypersensitivity skin reaction in the guinea-pig. Inhibitory activity was demonstrable in the efferent arc of the cell-mediated tuberculin and contact dermatitis (2,4-dinitrochlorobenzene) reactions. One of the compounds, 2-amino-9-benzyladenine, inhibited both turpentine-induced and histamine-induced inflammation in the skin. The toxicity and inhibitory activities of some of these compounds are discussed, and reference is made to the structurally related mercaptopurines.

Structure-activity profile of substituted purines and inflammation in the delayed hypersensitivity skin reaction

Substituted purines were tested for their effectiveness in inhibiting the delayed hypersensitivity skin reaction (DHSR) caused by tuberculin in the guinea-pig. Among the tested purines were naturally occurring derivatives of guanine and adenine, including cyclic AMP. Based on the structure-activity profile, a class of purines was identified, the members of which were very effective inhibitors of inflammatory aspects of the DHSR and are characterized by a benzyl group in position 9, an amino or alkylamino group in position 6, and various substituents in position 2. This class of 2-substituted-9-benzyladenines was more effective in the DHSR than some antimetabolites, particularly the structurally related mercaptopurines.