HLA class II polymorphism influences onset and severity of pathology in Schistosoma mansoni-infected transgenic mice

Abstract

Genetic factors that might influence susceptibility or resistance in naive individuals and early-stage pathology in schistosomiasis are difficult to study in clinical trials, since in areas where the disease is endemic the first contact with the parasite occurs most often at very early ages. Therefore, four strains (DR1.Abeta degrees, DR2.Abeta degrees, DQ8.Abeta degrees, and DQ6.Abeta degrees ) of major histocompatibility complex class II-deficient mice (Abeta degrees ), transgenic for different HLA alleles, have been used to evaluate the potential role of HLA class II polymorphism in the onset of the infection by Schistosoma mansoni. The survival rates and parasitological and immunological parameters after infection were evaluated and compared against the control values obtained with Abeta degrees mice. All four mouse strains used in this study were able to generate a specific immune response against S. mansoni antigens (cytokine production and antibody production). However, only mice expressing DR alleles survived until the chronic stage of the infection and were able to mount protective granulomatous response avoiding hepatic damage, presenting predominant gamma interferon production. In contrast, strains expressing DQ alleles revealed an impairment in generating effective granulomas, resulting in earlier death, which was associated with an impaired hepatic granulomatous response and liquefactic necrosis, reflecting the influence of HLA polymorphism in the establishment of protective response in the early stage of infection.

FIG. 1

Survival of HLA.Aβ° transgenic mice compared to Aβ° mice, exposed percutaneously to 50 cercariae of S. mansoni. Cumulative results of two independent experiments are represented. The number of mice used for each strain were: 14 for Aβ° (○), 15 for DR1.Aβ° (□), 9 for DR2.Aβ° (●), 13 for DQ6.Aβ° (×) and 9 for DQ8.Aβ° (▵).

FIG. 2

Histological analysis of hepatic tissues at 42 days p.i. stained with Masson trichrome stain (nuclei appear purple, cytoplasma is red, collagen is blue). (A) Control Aβ° mice. (B) Immunocompetent C57BL/6 mice. (C) DR1.Aβ° mice. (D) DR2.Aβ° mice. (E) DQ6.Aβ° mice. (F) DQ8.Aβ° mice. In panel A, hepatocytolysis is obvious, compared to the classical aspect of the granulomatous reaction in the immunocompetent control mice in panel B. DR1.Aβ° and DR2.Aβ° mice present typical granulomas, while DQ6.Aβ° mice show results similar to those of Aβ° mice. DQ8.Aβ° mice show a small but effective cellular reaction. Magnification, ×200.

FIG. 3

Collagen deposition at 42 p.i., expressed as a percentage of collagen increase in infected mice compared to healthy mice of the same age. Eight to ten mice/group were tested individually. The dotted line indicates collagen in uninfected individuals of the same age. The results are expressed as the mean ± the standard deviation and are representative of two experiments. ∗, Statistical analysis using the Student's t test gave P = 0.0056, P = 0.029, and P = 0.044, indicating a significant difference when comparing C57BL/6, DR1.Aβ°, and DR2.Aβ° mice, respectively, with Aβ° mice. No significant difference was observed between DQ8.Aβ° and Aβ° mice (P = 0.724).

FIG. 4

Parasite burden (A) and egg count (B) in the liver (expressed as eggs/worm pair/gram of liver) at 42 days p.i. Five to six mice/group were individually tested. The results are expressed as mean ± the standard deviation. ∗, Statistical analysis using the Student's t test gave P = 0.0239, indicating a significant difference between DQ8.Aβ° and Aβ° mice. No significant differences were observed in the adult worm burden or the numbers of parasite eggs trapped in the liver for the other transgenic strains.

FIG. 5

Cytokine production showing IFN-γ (A) and IL-4 (B) levels in the sera of infected transgenic and control Aβ° mice at 42 days p.i. Mice were individually tested. Cumulative results of three independent experiments are represented. The numbers of mice used for each strain were as follows: 11 for Aβ° mice (○), 19 for DR1.Aβ° mice (□), 18 for DR2.Aβ° mice (●), 17 for DQ6.Aβ° mice (×), and 12 for DQ8.Aβ° mice (▵). The choices of 10 pg/ml (IFN-γ) and 1 pg/ml (IL-4) is an arbitrary representation of sera detected below the cutoff of our ELISA test, calculated as the concentration at (mean ± 3 standard deviations) of the background. Statistical analysis using the Student's t test gave concentrations of IFN-γ in DQ6.Aβ° mice significantly lower than those in DR2.Aβ° mice sera (P = 0.026). Also, the amounts of IL-4 detected in DQ6.Aβ° mice were significantly lower than in DR2.Aβ° mice sera (P < 0.01).

FIG. 6

Specific IgG(H+L) antibodies production in sera (dilution, 1:100) of infected transgenic and control Aβ° mice to parasitic antigens: SOM (A), SWAP (B), and SEA (C). Seven to eight mice/group were individually tested. The results are expressed as the mean ± the standard deviation and are representative of two independent experiments.