Enhancement of experimental cutaneous leishmaniasis by Leishmania extract: identification of a disease-associated antibody specificity

Abstract

Background: Both Leishmania braziliensis and Leishmania amazonensis induce cutaneous disease when injected in the skin of BALB/c mice. However, L. amazonensis may also visceralize in that strain of mice, infecting mainly the liver and spleen. In addition, whereas BALB/c mice die with a progressive cutaneous disease when infected by L. amazonensis, the infection by L. braziliensis is spontaneously cured. In a previous work, we have found that intravenous injections of L. amazonensis amastigote extract (LaE) potentiated a L. braziliensis infection in BALB/c mice, and that this infection-promoting activity could be inhibited by the addition of protease inhibitors to the extract.

Methods: In order to detect markers of disease evolution, in the present work we analyzed the specificity of the anti-L. amazonensis antibody response of L. braziliensis-infected BALB/c mice injected intravenously with saline or LaE, supplemented or not with protease inhibitors, by the Western blot technique.

Results: IgG1 antibodies recognizing an antigen with apparent molecular weight of 116 kDa were specifically detected in BALB/c mice that had been turned susceptible to L. braziliensis infection by injections of LaE.

Conclusion: A Th2 immune response (IgG1 antibody-producing) against this 116 kDa antigen, therefore, could be associated with susceptibility to severe Leishmania infection.

Fig. 1

Lesion size and parasitism in mouse footpads six weeks after infection. The mice were treated with saline (Saline), saline supplemented with protease inhibitors (Saline + PI), or with L. amazonensis extract in the presence (LaE + PI) or absence (LaE) of protease inhibitors, as detailed in the Materials and Methods. a Lesion sizes, measured with a digital caliper as described in the Material and Methods. b Parasite numbers per milligram of tissue, as assessed by limiting dilution. Each symbol represent the value obtained from an individual mouse. The horizontal lines represent the median values of the results. *P ≤ 0.05; **P ≤ 0.01 (Kruskal-Wallis’s test followed by Dunn’s post test)

Fig. 2

Reactivity against L. amazonensis antigens, as assessed by Western blot, of IgG1 antibodies in the sera of BALB/c mice that had been injected with L. amazonensis extract and infected with L. braziliensis. The sera were from blood samples collected five weeks after infection. The infected mice were treated with saline (Saline; lanes 2 to 6), L. amazonensis extract supplemented with protease inhibitors (LaE + PI, lanes 7 to 11) or unsupplemented L. amazonensis extract (LaE, lanes 12 to 16), as detailed in the Materials and Methods. The result obtained with the serum of a naïve mouse is shown in lane 1. The positions of molecular weight markers are shown on the left of the figure

Fig. 3

Reactivity against L. amazonensis antigens, as assessed by Western blot, of IgG2a antibodies in the sera of BALB/c mice that had been injected with L. amazonensis extract and infected with L. braziliensis. Sera were from blood samples collected five weeks after infection. The infected mice were treated with saline (Saline; lanes 2 to 6), L. amazonensis extract supplemented with protease inhibitor (LaE + PI, lanes 7 to 11) or unsupplemented L. amazonensis extract (LaE, lanes 12 to 16), as detailed in the Materials and Methods. The result obtained with the serum of a naïve mouse is shown in lane 1. The positions of molecular weight markers are shown on the left of the figure