Experimental cutaneous leishmaniasis. IV. Selective suppression of cell-mediated immunity during the response of guinea-pigs to infection with Leishmania enriettii

The purpose of this study was to determine whether suppression of acquired, cell-mediated immunity occurred during the course of cutaneous leishmaniasis of the guinea-pig. In order to do this, groups of animals were infected with amastigotes of Leishmania enriettii in doses ranging from 10¹ to 2 × 10⁸ organisms. The clinical course of primary and metastatic infection was followed for up to 30 weeks and the immunological response was examined by skin tests of hypersensitivity to soluble leishmanial antigens, by detection of circulating antibody, and by determining the resistance of animals to reinfection with fresh organisms.

With increasing inoculum size the incubation period (for the establishment of a primary lesion) diminished from 4 weeks (10¹ organisms) to 1 week (2 × 10⁸ organisms). Large inocula (2 × 10⁸) led to large ulcerated primary lesions with widespread metastases and death of some animals in the group, but no evidence of visceralization. With increasing dose of organisms, there was increasingly rapid development of delayed hypersensitivity and of antibody as detected by immunofluorescence; thus there was no evidence that high inocula produced immunological tolerance. With inocula >10⁵, a characteristic and selective depression of delayed hypersensitivity occurred when primary lesions were well developed and when metastatic infection was well advanced. Surviving animals recovered their delayed hypersensitivity as primary and metastatic lesions healed. After healing of the primary lesions, animals in all groups were fully resistant to reinfection, even though some of them bore persistent metastases.

It was concluded that the immunosuppressive effects of heavy infecting inocula were due to desensitization of rapidly acquired, cell-mediated immunity rather than to the induction of immunological tolerance. It is suggested that this mechanism might underlie certain features of disseminated leishmaniasis in man.

Serum IgE levels in protozoal and helminthic infections

Serum IgE concentration is measured, according to the Rowe modification of the Mancini technique, in non-atopic patients suffering from various helminthic or protozoal infections. Our results indicate that the IgE level is often raised in parasitosis with prominent tissue phases and remains normal with helminths whose life is restricted to the lumen of the digestive tract. In addition, our observations show that, with helminthic or protozoal infestations, the serum IgE level tends to increase significantly and rapidly following a specific treatment of the parasitosis. Afterwards, the serum IgE level decreases slowly and may return to the normal in a few months. Thus, repetitive evaluations of serum IgE concentrations, before and after therapy, appear to be of a diagnostic value in the cases where a vague clinical picture is suggesting an helminthic parasitosis.

Pharmacokinetic and toxicological studies of antimony dextran glycoside (RL-712)

1. The absorption, tissue distribution and excretion of antimony dextran glycoside (RL-712) has been studied in normal rodents.2. Some organs in the body, especially liver and spleen, retain large amounts of antimony for considerable periods of time. Excretion of antimony in the urine was low and only about 10-12% of the dose administered was excreted within the first 48 hours.3. Blood levels were maintained for at least 3 days after a single intramuscular dose to rabbits, corresponding to 14 mg Sb/kg body weight.4. Toxicity studies and tests on foetal toxicity in mice and rats, respectively, showed no abnormalities.5. The possible value of RL-712 in the prophylaxis and treatment of leishmaniasis is discussed.

Experimental cutaneous leishmaniasis. II. Effects of immunosuppression and antigenic competition on the course of infection with Leishmania enriettii in the guinea-pig

Intradermal inoculation of the guinea-pig with Leishmania enriettii results in a self-healing cutaneous lesion which provides a laboratory model of human cutaneous leishmaniasis and which is dominated by cell-mediated immunological responses (Bryceson et al., 1970). In this study we sought to design experimental situations resembling non-healing forms of cutaneous leishmaniasis in man and to determine whether these experimental situations were accompanied by abnormalities in the immunological response to infection. This paper describes three procedures which impair the resistance of guinea-pigs to leishmanial infection: (i) induction of partial immunological tolerance to leishmanial antigen; (ii) systemic injection of anti-lymphocyte serum (ALS); and (iii) regional antigenic competition produced by multiple injections of bacterial adjuvants.

Injection of soluble leishmanial antigen (PSA) during the third week of foetal life suppressed resistance to neonatal infection with L. enriettii; local infections were severe and were accompanied by metastatic spread and by impaired development of delayed hypersensitivity (DH). Injection of PSA into the 6-week foetus and into the adult guinea-pig led to impaired DH after leishmanial infection, but resistance to infection was only slightly suppressed. Transient impairment of DH was induced by a short injection course of adult animals with ALS during the first 3 weeks of infection, which resulted in large primary lesions with temporary metastatic spread.

Multiple regional injections of tubercle- and corynebacterial-adjuvant emulsions markedly suppressed resistance to subsequent leishmanial infection; large ulcerative lesions were accompanied by widespread nodular metastases, the unusual appearance of haemagglutinating antibody, and death of some animals.

There was no impairment of DH to PSA; in fact, this was temporarily enhanced during the first 6 weeks of leishmanial infection of the tubercle-adjuvant group. This suppression of resistance could not be attributed to systemic desensitization of DH to bacterial antigen or to the local sclerosing effects of adjuvant emulsion; the term `regional antigenic competition' was therefore employed. Both the induction of partial tolerance and the injection of ALS selectively impaired paracortical responses in lymph nodes draining leishmanial infections; however, in regional antigenic competition the lymph nodes were infiltrated with macrophages but both follicular and paracortical responses were prominent.

Suppression of resistance to L. enriettii was not related simply to impairment of DH; for there was overall dissociation of protective, allergic and antibody responses in these suppressed animals. The relationship of cellular immune mechanisms to cutaneous leishmaniasis was viewed in two ways. First, it was inferred that resistance of guinea-pigs to L. enriettii requires both successful induction of cell-mediated immunity and functional integrity of the regional lymphoid system at the time of infection. Second, it was suggested that nonhealing forms of human cutaneous leishmaniasis may arise from defective coordination of surveillance, inflammatory and adjuvant functions of the cellular immune response to leishmanial antigens. It was concluded that interference with cellular immune responses in the guinea-pig led to experimental infections which resembled some features of more generalized cutaneous leishmaniasis in man.

Experimental cutaneous leishmaniasis. 3. Effects of thymectomy on the course of infection of CBA mice with Leishmania tropica

This paper describes the course of infection and the immunological response in thymus-deprived and normal CBA mice after intradermal inoculation with promastigotes of L. tropica.

Infection of normal mice resulted in the development of a cutaneous ulcer healing within 12 weeks. As the infection progressed and the draining lymph nodes increased in weight, changes in the paracortical and follicular regions were accompanied by the development of delayed hypersensitivity and the production of antibodies detectable by immunofluorescence and a parasite agglutination test.

Lesions in thymectomized irradiated mice healed more slowly and the draining lymph nodes were smaller than in normal mice. Follicular reactions were feeble and paracortical activity depressed. The most noticeable feature of these lymph nodes was a persistent and intense macrophage infiltration. Delayed hypersensitivity and antibodies detectable by immunofluorescence were correspondingly low; but parasite agglutinating antibody was not depressed. The course of infection and immunological response of a control group of sham thymectomized, irradiated mice resembled that of normal mice.

These experiments indicate that thymus-dependent cell populations play an important role in the response of mice to infection with L. tropica.

Immunology of leishmaniasis

Knowledge of the immunological basis of the leishmaniases and of the host's response is fragmentary and largely pragmatic. This paper reviews certain conceptual and clinical aspects of the immunology of these diseases. Consideration is given to man's natural resistance and his ability to acquire resistance from natural infections and from vaccination. The age-distribution of infection in different populations is discussed in relation to the effects that interaction between the parasite and its intermediate host may have on its infection characteristics and virulence.Studies in the USSR of differences in virulence among 30 human strains and 39 rodent strains are reported. The rodent strains showed a broader range of virulence than did the human isolates. Serological tests for determining species relationships among the leishmaniae are generally nonspecific, but work concerned with the development of the antiserum-culture test is reviewed. Species identification and the recognition of new forms, perhaps with different infection characteristics, is, nevertheless, of the utmost importance in the prevention and treatment of the disease.The review concludes with a discussion of functional immunity and hypotheses of the immune process in leishmaniasis.

Immunity in cutaneous leishmaniasis of the guinea-pig

This paper describes the course of infection and development of immunity in guinea-pigs after intradermal inoculation of Leishmania enriettii, and the use of in vivo and in vitro techniques to characterize the immunological response to infection and artificial immunization.

Inoculation of 10⁶ amastigotes into the ear produced a nodule which ulcerated in 2–3 weeks and healed in 8–16 weeks. 8% of animals developed cutaneous metastases which healed with the original lesions. Histology of the primary lesions showed epidermal necrosis overlying a mass of parasitized macrophages which, after 4–6 weeks, became surrounded and infiltrated by lymphocytes. Histological changes in the draining lymph node began after 3 days and proceeded for 6 weeks; both germinal centres and paracortical areas were hyperplastic and the medulla contained many plasma cells. Superinfection produced an `isophasic' lesion, but reinfection after healing elicited only a delayed hypersensitivity response. Artificial immunization with soluble and insoluble antigenic extracts of L. enriettii in Freund's complete adjuvant partially protected against infection; extracts of other leishmanial species failed to protect. Immunological paralysis, attempted with intravenous injections of soluble antigen, increased the severity of subsequent infection.

Both infection and immunization were accompanied by delayed hypersensitivity which could be transferred passively by lymphoid cells. Cell-mediated immunity was studied in vitro by the ability of soluble leishmanial antigens to transform lymphocytes, to inhibit macrophage migration, and to induce the production of lymphokine factors from lymphocytes of sensitized animals. A target cell system was devised in which sensitized lymphocytes destroyed monolayers of parasitized macrophages. Cross reactivity of leishmanial with mycobacterial antigens was shown in skin tests and in target cell destruction, but not in cell transfer or in the other cell culture systems. The phagocytic activity of peritoneal macrophages from recovered animals was increased for homologous but not for heterologous species of Leishmania; the growth of ingested organisms was not however reduced.

Circulating antibodies were not demonstrated by passive cutaneous anaphylaxis, or by agglutination of antigen coated sheep erythrocytes, in the sera of infected or convalescent animals, although some convalescent animals showed active cutaneous anaphylaxis. However, antibodies were demonstrated by both these techniques in immunized animals, which also showed anaphylactic and Arthus hypersensitivity when skin tested with the soluble antigens.

The results are taken to indicate that cellular mechanisms are prominent in the development of immunity of the guinea-pig against L. enriettii, and ways in which the host may eliminate the parasite are discussed. It is concluded that this model provides an experimental counterpart of human cutaneous leishmaniasis and that it is suitable for the analysis of the role of cell-mediated specific immunity in resistance to intracellular infection.