[Comparative study of the antigenic properties and virulence of Leishmania clones (Trypanosomatidae, Leishmania)]

A relation between antigenic properties and virulence of Leishmania clones were studied. The clones were obtained from a naturally infected sandfly (Phlebotomus of the group caucasicus) caught in the burrow of great gerbil in Turkmenia. Antigenic properties of the clones were studied by means of Adler's test (Safjanova's modification); the virulence of the clones was studied on golden hamsters by means of standard technique. There was revealed heterogenicity of the Phlebotomus strain of Leishmania, in it there were found clones identical serologically to Leishmania donovani and L. major and a clone close in antigenic respect to Leptomonas pessoai. At the experimental infection of hamsters with a heterogeneous Phlebotomus strain their mixed infection with the two above mentioned Leishmania species was first observed. Serologically identical Leishmania clones can differ essentially in their virulence. A high stability of antigenic properties of Leishmania clones has been revealed. At the same time the virulence of clones is characterized by variability as towards its increase (the passing of a clone on hamsters) so towards its fall (cultivation of a clone in vitro, on nutrient medium).

Immune responses in parasitic diseases. Part A: general concepts

Parasitic infections are incredibly varied and distinct in terms of interactions between hosts and pathogens as well as in complexity of life cycle, host range, vector or intermediary host requirements, forms of reproduction, and elicited response. A number of protozoan parasites are intracellular pathogens capable of surviving and multiplying within microbicidal cells such as macrophages. In contrast, nematodes generally do not multiply within the host, a trait that dramatically alters the epidemiologic, clinical, and immunologic consequences of infection. Parasites have acquired apparently effective mechanisms for escape from normal host defenses and clearance. These mechanisms may be classified as antigenic mimicry, antigenic depletion, antigenic variation, immunologic indifference, immunologic diversion, and immunologic subversion. A determination of the importance and relevance of these subterfuges to parasitic infection in humans and to therapeutic or prophylactic strategies is of the utmost urgency.

Levamisole and immune response phenomena in cutaneous leishmaniasis

Levamisole has been successfully used therapeutically in twenty-eight cases of chronic cutaneous leishmaniasis. It is suggested that repeated sandfly bites not initiating a clinical lesion may immunize against later infection by the formation of blocking antibodies to Leishmania tropica or by denying the parasite a locus in which it can become established. Late-appearing lesions in natives of endemic areas should raise the suspicion of impaired immunity from systemic disease such as malignancy.

Mechanisms of immunity to leishmaniasis. IV. Significance of lymphatic drainage from the site of infection

The course of Leishmania tropica infection in BALB/c and B6D2 mice has been followed after injection of the parasite at different sites. The effect of interruption of lymphatic drainage from the inoculation site has also been examined. In both strains of mice, more severe disease resulted from infection induced in the shaved rump, as compared to infection in the footpad. The removal of the popliteal lymph node prior to footpad infection, caused a considerable exacerbation of the disease. Such increased severity and associated with an initial inhibition of the induction of delayed-type hypersensitivity and a delay in the emergence of acquired resistance. Lymph node removal did not however compromise the effector arm of the acquired immune response, nor prevent the eventual suppression of delayed hypersensitivity that has been shown to occur in the BALB/c, during leishmanial infection.

[Cutaneous leishmaniasis: clinical and immunopathological aspects]

Foi visto nesta revisão que os parasitas do gênero Leishmania induzem uma variedade de respostas complexas nos hospedeiros vertebrados, efetuadas e/ou moduladas pelo seu sistema imunológico. Foi também salientado que o destino da Leishmania no interior de macrófagos depende de relações particulares parasito-hospedeiro, envolvendo não apenas as propriedades intrísecas do parasita, mas também as características, geneticamente determinadas, da cédula hospedeira ou das suas interações com outras células imunocompetentes. Atráves de uma revisão das evidências consubstanciando essesconceitos, os mesmos foram aplicados na descrição do espectro clínico e imunopatológico da doença humana, particularmente das leishmanioses cutâneas e mucocutâneas do Novo e do Velho Mundo. Finalmente, baseando-se nos resultados obtidos em modelos experimentais de leishmaniose cutânea, os quais reproduzem os achados das formas resolutiva e persistentes da doença humana, o autor apresenta uma análise esquemática da evolução das características histopatológicas das lesões leishmanióticas.

Immunologic regulation of experimental cutaneous leishmaniasis. V. Characterization of effector and specific suppressor T cells

Resistant CBA mice infected with Leishmania tropica promastigotes develop concomitant and convalescent immunity against reinfection. This can be adoptively transferred by splenic and lymph node T cells with a threshold dosage of 1 to 2.5 x 10(7). The effector cells are of Thy-1+, Lyt-1+2- phenotype. The same immune cell population also adoptively transfers specific DTH to L. tropica, which is restricted by the major histocompatibility complex. On the other hand, highly susceptible BALB/c mice infected with L. tropica develop antigen-specific suppressor T (Ts) cells (previously shown to inhibit the induction and expression of DTH), which are capable, on transference, of reversing the healing of lesions induced by prior sublethal irradiation of BALB/c mice. As few as 10(6) of these T cells are effective in abrogating the potent prophylactic effect of 550 rad. The Ts cells are of Thy-1+, Lyt-1+2-, and I-J- phenotype. Sublethally irradiated and infected BALB/c mice produce antibody responses quantitatively and isotypically similar during the critical first 40 days after infection whether or not they are injected with 10(7) Ts cells (nonhealing vs healing). Thus, impairment of DTH and curative immune responses in BALB/c mice cannot be attributed to a helper function of these Thy-1+, Lyt-1+2- cells for the formation of suppressive antibody.

Vaccination of the African white-tailed rat, Mystromys albacaudatus, with sonicated Leishmania braziliensis panamensis promastigotes

The usefulness of sonicated Leishmania braziliensis panamensis promastigotes for vaccination was evaluated in Mystromys albacaudatus, the African white-tailed rat. Thirty-two animals received three intradermal injections of 2 x 10(6) sonicated promastigotes derived from L. braziliensis panamensis at weekly intervals. One month after completion of the immunization schedule, the experimental group of animals was challenged in vivo with 2 x 10(6) live L. braziliensis panamensis promastogotes. At the same time, a matched group of 40 control animals was similarly challenged. Within 2 months, 35 of the 40 animals (87.5%) the control group developed ulcers, while only 14 of 32 previously vaccinated animals (43.7%) developed ulcers at the site of challenge within the same time period. The remaining 18 vaccinated animals (56.2%) remain free from ulcers 7 months after challenge. When lymphocytes from the spleens of vaccinated and control animals were challenged in vitro with antigen derived from sonicates of varying numbers of promastigotes, only cells from immunized animals responded vigorously to the antigenic challenge, a response which was not enhanced by the addition of immune antiserum to the reaction.

Specific inhibition of lymphocyte-proliferation responses by adherent suppressor cells in diffuse cutaneous leishmaniasis

Diffuse cutaneous leishmaniasis is characterized by multiple nonulcerative skin lesions. Histologically, these lesions are dominated by vacuolated, heavily infected macrophages, with only a few lymphocytes present. A unique focus of diffuse cutaneous leishmaniasis is present in the Dominican Republic. We studied four patients with this disease. None had a delayed reaction to leishmanial antigen on skin tests. The total numbers of lymphocytes and T cells were normal. None of these patients had a lymphocyte-proliferation response to leishmanial antigens, although their responses to other antigens were normal. Adding indomethacin to cultures or decreasing the number of adherent cells by passage of cells over nylon wool reconstituted the lymphocyte responses to leishmanial antigens. Thus, our studies demonstrate that patients with diffuse cutaneous leishmaniasis have a selective anergy to leishmanial antigen, and that an adherent suppressor cell is one mechanism by which this selective immunosuppressive state is modulated.

Macrophage induction of T-suppressor cells in pesticide-exposed and protozoan-infected mice

The use of infectious pathogens has allowed the detection of the development of synergism between pathogens and ubiquitous environmental chemical contaminants. This synergism has been demonstrated to result in a state of immunosuppression which either did not occur in the independent and singular presence of the chemical or pathogen and/or was greater than additive when both were combined. The immunosuppression was distinct with regard to the organochloride used and, therefore, is not a ubiquitous characteristic of all organohalides. The production of a macrophage soluble factor which appeared to induce T-suppressor cells was demonstrated in hepatic Kupffer cells from mice administered 5 ppm of dieldrin for 10 weeks and then infected with Leishmania tropical promastigotes. The factor was not generated in mice administered dieldrin and infected with malaria nor in mice administered only dieldrin nor in mice only infected with Leishmania. Additional studies revealed a profound impairment in macrophage antigen processing with macrophages obtained from mice administered dieldrin. The use of pathogen models may allow the immunosuppressive potential of environmental chemical contaminants to be expressed in a more sensitive manner.

Intralesional plasma cells and serological responses in human cutaneous leishmaniasis

Intralesional plasma cells and serological responses were investigated in 20 Brazilian cases of cutaneous leishmaniasis. Plasma cell numbers varied from less than 10% to more than 50% of cells in inflammatory infiltrates, in general with greater numbers of such cells present in lesions of longer duration. Direct fluorescence examination with anti-IgG, -IgA and -IgM sera of trypsin-treated sections of formalin-fixed biopsy tissue revealed that most intralesional plasma cells contained IgG. Russell bodies were detected in eight cases, in seven of which these bodies fluoresced only with anti-IgM serum. There was no correlation between serum levels of total IgG, IgA and IgM (detected by radial immunodiffusion) or antileishmanial antibodies (detected by class-specific indirect immunofluorescence and by direct agglutination with and without 2-mercaptoethanol) and numbers of intralesional plasma cells of the same globulin class. No striking or consistent alterations in complement components were noted in the serum of these patients.

Immunogenetics of susceptibility to leprosy, tuberculosis, and leishmaniasis. An epidemiological perspective

The literature on the genetic regulation of susceptibility in leprosy, tuberculosis, amd leishmaniasis is critically reviewed. Of the three groups of diseases, leprosy has received the most attention from the standpoint of human genetics. There is now evidence that genetic factors, some of them HLA-linked, play a role in tuberculoid leprosy. However, the evidence leaves considerable room for environmental determinants in addition to genetic background. Several twin studies of tuberculosis have favored some genetic factors in clinical tuberculosis, but their evidence is mitigated by the many biases underlying such studies. Though very little work has been done on the genetics of leishmaniasis in man, experimental studies in mice have begun to unravel mechanisms controlling successive steps in the course of both L. donovani and L. torpica infections. It is suggested that future work should concentrate on moving from genetics to biochemical genetics in the mouse, should extend family studies in conjunction with markers in man, and should place high priority on confirmation of reported leprosy type discordance among monozygous twins.

Intracellular replication and lymphokine-induced destruction of Leishmania tropica in C3H/HeN mouse macrophages

C3H/HeN resident peritoneal macrophages in suspension culture supported continuous replication of L. tropica amastigotes; the total number of intracellular parasites increased 8- to 10-fold over 96 hr in culture. Lymphokine treatment of macrophages markedly affected intracellular replication of the Leishmania. Cultures treated with lymphokines before exposure to L. tropica were more resistant to infection, and 35% fewer cells contained intracellular amastigotes compared to medium-treated controls. Lymphokine-pretreated cells that became infected also inhibited the replication of intracellular amastigotes. Macrophage cultures treated with lymphokines after infection exhibited potent microbicidal activity; 75 to 80% of macrophages were free of intracellular parasites by 72 hr. Fractionation of lymphokine supernatants by Sephadex G-100 demonstrated 3 areas of activity for the induction of macrophage intracellular killing (130,000, 45,000, less than or equal to 10,000 daltons); one of these activity peaks (45,000-m.w. lymphokine(s)) also induced increased resistance to infection with L. tropica.

Experimental cutaneous leishmaniasis. I. Nonspecific immunodepression in BALB/c mice infected with Leishmania tropica

Leishmania tropica in BALB/c mice causes a fatal infection accompanied by the development of multiple metastatic lesions. Spleen cells from these mice were shown to have depressed proliferative responses to concanavalin A (Con A), phytohemagglutinin (PHA), and lipopolysaccharide (LPS). Coinciding with this immunodepression was the development of a cell population capable of suppressing normal spleen cell responses to Con A. This suppressor cell activity was first observed at 6 wk and was present throughout the remainder of the infection. At 12 wk the suppressor cells could be removed by Sephadex G-10 passage or carbonyl iron treatment; however, Sephadex G-10 passage could not reverse the suppression at 18 wk. Indomethacin, a prostaglandin synthetase inhibitor, was found to abrogate the activity of the adherent suppressor cell, suggesting that prostaglandin production may be involved in the immunosuppression seen in these mice. In addition, Sephadex G-10 passage and indomethacin were found to markedly augment spleen cell responses to leishmanial antigen, indicating that the adherent suppressor cell is capable of regulating specific immunologic responses.

Evaluation of antigens for the serodiagnosis of kala-azar and oriental sores by means of the indirect immunofluorescence antibody test (IFAT)

Antigens and corresponding sera were collected from travellers with leishmaniasis returning to Germany from different endemic areas of the old world. The antigenicity of these Leishmania strains, which were maintained in Syrian hamsters, was compared by indirect immunofluorescence (IFAT). Antigenicity was demonstrated by antibody titres in 18 sera from 11 patients. The amastigotic stages of nine strains of Leishmania donovani and four strains of Leishmania tropica were compared with each other and with the culture forms of insect flagellates (Strigomonas oncopelti and Leptomonas ctenocephali). Eighteen sera from 11 patients were available for antibody determination with these antigens. The maximal antibody titres in a single serum varied considerably depending on which antigen was used for the test. High antibody levels could only be maintained when Leishmania donovani was employed as the antigen, but considerable differences also occurred between the different strains of this species. The other antigens were weaker. No differences in antigenicity between amastigotes and promastigotes of the same strain were observed. It is important to select suitable antigens. Low titres may be of doubtful specificity and are a poor baseline for the fall in titre which is an essential index of effective treatment.

Resistance to cutaneous leishmaniasis in genetically susceptible BALB/c mice

When injected cutaneously with promastigotes of an isolate of Leishmania tropica, BALB/c mice develop progressive cutaneous disease whereas lesions in BALB/c.H-2k mice heal after several weeks. Lesions in BALB/c mice injected into deep subcutaneous tissues with promastigotes are less obvious early but much more prominent later than in mice after strict intradermal injection. BALB/c mice injected with Corynebacterium parvum together with a preparation of frozen and thawed infected macrophages are more resistant to cutaneous disease than mice injected with either adjuvant or crude antigen mixture alone. Results of these experiments, and those on other mouse strains reported previously, will aid in the choice of mouse and injection regime to be used in testing the efficacy of isolated L. tropica antigens as vaccines.

Single gene control of resistance to cutaneous leishmaniasis in mice

A series of inbred, congenic resistant, and hybrid strains of mice were intradermally inoculated with 10(6) promastigotes of Leishmania tropica. These mice were divided into susceptible and resistant groups using the criteria of lesion size, development of metastatic foci and skin-test reactivity. At 16 weeks of infection, resistant strains A/J, DBA/1J, AKR/J, CBA/J, C3H/HeJ, NZB/BINJ, C57BL/6J, C57BL/10Sn, B10.D2, B10.129(10M), and B10.CE(30NX) had completely resolved their lesions, while susceptible SWR/J and BALB/cJ mice demonstrated large, nonhealing cutaneous lesions. In addition, BALB/cJ developed metastatic lesions on the extremities which progressively increased in size. A11 BALB/cJ and SWR/J mice died by 7 1/2 months of infection. The BALB/cJ female x C57BL/6J male F1 hybrid behaved in an intermediate fashion showing a slower expansion of cutaneous ulcers and a delayed development of metastatic foci, however, the infection ultimately proved fatal. The F2 generation could be separated into three distinct groups:resistant, intermediate, and susceptible mice with a lesion size distribution pattern in conformity with a 1:2:1 ratio. Male/female susceptibility differences were not noted. These data indicated that development of acquired resistance may be under the control of a single, autosomal gene. The gene did not appear to be H-2-, Ir-2-, or H-11-linked as is seen with Leishmania donovani infections.

[Immunodiagnostic findings in sera of patients with leishmaniasis, Chagas' disease, malaria and amebiasis in endemic regions of Venezuela (author's transl)]

66 serum samples from patients suffering from mucocutaneous leishmaniasis (20), Chagas' disease (12), malaria (16) or amebiasis (18) were collected and examined with five different protozoic antigens (L. donovani, T. cruzi, P. fieldi, P. falciparum, E. histolytica) by means of the indirect fluorescent antibody test, the complement fixation test, the indirect hemagglutination test and the latex agglutination. Cross-reactions were observed only between the sera from patients with leishmaniasis and Chagas' disease, both groups, however, showed stronger reactions with the homologous antigen. There were no cross-reactions among the other antigens and antibodies. The results obtained in this study together with facts already proved by literature show the usefulness of the employed antigens for epidemiological surveys.

Nonspecific immunodepression and protective immunity in mice infected with Leishmania mexicana

C57BL/6 mice infected with Leishmania mexicana showed depression of the in vitro immunoglobulin M-plaque-forming cell response to sheep erythrocytes. Immunodepression was present 3 weeks after inoculation and was maximal at 11 weeks. Thereafter, there was a gradual return to normal immunoresponsiveness correlated with the resolution of lesions. At the time of maximal immunodepression, spleen cells from infected mice diminished the plaque-forming cell response to sheep erythrocytes of normal spleen cells. On the other hand, specific responses, as exemplified by protective immunity to a challenge infection and delayed hypersensitivity responses to parasite antigens, were apparently unaffected. These responses were both present in mice bearing primary lesions and were maximal in recovered mice. The significance of these findings is discussed in relation to a current hypothesis on parasite-induced immunodepression.

Recognition of protozoan parasites by murine T lymphocytes. II. Role of the H-2 gene complex in interactions between antigen-presenting macrophages and Leishmania-immune T lymphocytes

The proliferative response of nylon wool purified, primed lymph node cells to L. tropica parasites in vitro was found to be restored by the addition of either syngeneic or allogeneic adherent spleen cells as a putative source of macrophages. These results suggested a lack of H-2 restriction in Leishmania-specific T cell responses. However, when T cell blasts generated in vitro in response to the parasite were separated on Percoll density gradients and subsequently maintained for 4 days in the presence of TCGF, their response to L. tropica was found to be strictly dependent on the presence of syngeneic spleen cells. Further studies using congenic recombinant mice demonstrated that proliferation of a parasite-specific blasts required the presence of spleen cells compatible with the responding cells in the I-A region of the MHC. This requirement for I-A compatible adherent cells in the spleen cell populations was further confirmed by a lack of proliferative responses in the presence of spleen cells treated with monoclonal anti-la antibodies and complement. Leishmania-immune F1 blasts responding to the parasite in the context of either parental la-bearing accessory cell could be obtained by positive selection from a F1 hybrid responding cell population. Using flow microfluorometry, the T cell phenotype of the L. tropica-specific blasts was determined to be Thy-1+, lyt-1+, and Lyt-2-.

Expression of Leishmania antigen on the surface membrane of infected human macrophages in vitro

Resolution of leishmaniasis is associated with host immunological responsiveness to parasite antigens. In clinical disease, leishmania are found as amastigotes contained with macrophages. We investigated the possibility that Leishmania antigens are expressed on the infected macrophage surface by reacting infected macrophages with antibody to Leishmania. In vitro-infected human monocyte-derived macrophages were labelled with antibody to amastigotes when examined with immunofluorescent or immunoelectron microscopic techniques. Infected macrophages were poorly labelled by antibody to promastigotes (insect forms of Leishmania). Certain antisera that reacted with the surface membranes of amastigotes did not label the infected macrophage surface. These results indicate that human macrophages infected in vitro express Leishmania amastigote antigen(s) on their surface membranes, that such antigen(s) may not be present in large quantities in promastigotes, and that certain antigen(s) on the amastigote surface are not expressed on the surface membranes of infected macrophages.

Immunological regulation of experimental cutaneous leishmaniasis. IV. Prophylactic effect of sublethal irradiation as a result of abrogation of suppressor T cell generation in mice genetically susceptible to Leishmania tropica

The overwhelming susceptibility of BALB/c mice to infection with Leishmania tropica can be substantially reversed by immediately prior sub-lethal irradiation. This is related to radiation dosage, and at 550 rad, causes 60 percent complete cures and only 19 percent (instead of 100 percent) incidence of progressive disease. Irradiation 10 d before infection is only weakly prophylactic, whereas 10 d after is without effect. Control of lesion development is only apparent after the first 30 d, coincident with the analogous onset previously found in resistant strains and adult thymectomized, x-irradiated, bone marrow-reconstituted BALB/c mice. Instead of the specific suppression of DTH characteristic of L. tropica infection in the BALB/c strain, healed irradiated mice express strong anti-leishmanial DTH reactivity and resistance to reinfection. T cells from these mice transfer DTH reactivity which is suppressed by admixture with cells from nonhealed, nonreactive donors. Irradiated BALB/c mice again develop inexorable disease progression, after its transient arrest, when they are reconstituted with normal T cells. When the T cells are derived from uncontrollably-infected donors, the susceptibility regained is indistinguishable from that of normal mice. B cells do not modify the prophylactic effect of 550 rad, whereas T cells from healed mice confer strong protective immunity throughout the initial phase. Regression or progression of disease correlates completely with DTH reactivity in all these groups. Although BALB/c mice express an extreme level of genetic susceptibility to L. tropica infection, they are nevertheless capable of mounting a curative cell mediated immune response. That this is ineffective during pathogenesis of the disease was previously associated correlatively with potent specific suppressor T cell generation, which is now shown to be preventable by prior irradiation. Most important, however, a causal role for these cells in vivo has been demonstrated directly by reconstitution.

Immunological regulation of experimental cutaneous leishmaniasis. 2. Studies with Biozzi high and low responder lines of mice

Susceptibility to Leishmania tropica was studied in Biozzi 'high' (Ab/H) and 'low' (Ab/L) responder mice of Selections I and III which, although originally selected with heterologous erythrocytes and Salmonella flagellar antigens respectively, both show non-specific separation of antibody responses. Ab/H Sel I produce only small lesions, even with the largest infecting dose, which heal after 2 months with minimal antibody responses. Specific delayed-type hypersensitivity (DTH) levels found in both are normal and equivalent. (Ab/H x Ab/L)F1 mice behave intermediately. A smaller inter-line difference is only detectable in Sel III with lower infecting doses. Both Ab/L and Ab/H mice given high doses develop chronic non-healing disease. These results imply that spontaneous resolution of cutaneous L. tropica lesions during the immune phase is independent of humoral antibody. While the great resistance and slower development of lesions found in Ab/L Sel I are entirely consistent with the macrophage 'hyperactivity' characteristic of the line, attempts to demonstrate this in vitro with comparisons of infected peritoneal exudate have been inconclusive so far.

Identification and characterization of protein antigens of Leishmania tropica isolates

Promastigotes of 4 Leishmania tropica isolates were biosynthetically labeled with 35S-methionine or surface radioiodinated, and the detergent lysates were analyzed by 2 dimensional gel electrophoresis. The protein patterns of cytoplasmic and membrane proteins detected in two independent isolates from simple cutaneous leishmaniasis cases were similar to each other, but were different from 2 isolates taken over a 20-yr interval from a case of leishmaniasis recidiva. The analysis of radioiodinated membrane proteins of L. tropica promastigotes revealed a simple pattern of 6 to 7 labeled major proteins and some minor ones. Unlike cytoplasmic proteins, membrane proteins were highly resistant to digestion by proteases. Partial cleavage of radioiodinated surface proteins by staphylococcal V-8 protease in the presence of 4.5 M urea and peptide mapping confirmed the presence of shared and isolate-specific proteins. The significance of these findings for the classification of Leishmania spp. and the pathogenesis of the different disease states that they cause are discussed.

Systemic infection of Leishmania tropica (major) in various strains of mice

The spleen cells of different strains of mice were cultured and examined for the presence of viable promastigotes one to three months following a cutaneous inoculation of 1 to 2 X 10(6) promastigotes of Leishmania tropica (major). The spleen cultures of all five strains tested (BALB/c, DBA/3, C3H, CBA and C57B1/6) contained organisms. Viable parasites were present in the spleen of resistant strains (C3H, CBA, C57B1/6) even after recovery from their cutaneous lesion. The possible implication of this finding in the long lasting immunity observed in this disease is discussed.

Susceptibility of Aotus trivirgatus to Leishmania braziliensis and L. mexicana

Two Aotus trivirgatus (owl monkeys) were infected experimentally with Leishmania braziliensis and two with L. mexicana strains of Panamanian origin in a pilot study to determine the susceptibility and the course of infection of cutaneous leishmaniasis in this primate species. Montenegro skin tests performed on all animals prior to parasite inoculation were negative. A standardized inoculum of promastigotes was injected intradermally on the nose of each monkey. All of the animals developed infections which lasted from 3.5 to 8.5 months. Depigmentation developed at the site of the inoculation in all of the subjects. The severity of the resulting lesions was greater in the animals infected with L. braziliensis. Positive skin tests developed in three A. trivirgatus at days 62, 76, and 139 postinoculation, respectively. An explanation for the negative skin test in the fourth animal is discussed.