CD4(+) T cells which react to the Leishmania major LACK antigen rapidly secrete interleukin-4 and are detrimental to the host in resistant B10.D2 mice

Abstract

Leishmania major induces the rapid production of interleukin-4 (IL-4) in both susceptible BALB/c and resistant B10.D2 mice. In both strains, IL-4 is produced by T cells which react to the parasite LACK (for Leishmania homolog of the receptor for activated C kinase) antigen. The rapid production of IL-4 in B10.D2 mice does not confer susceptibility but results in increased parasite burdens.

FIG. 1

Early accumulation of IL-4 mRNA in susceptible and resistant mice infected with L. major. Mice of the indicated inbred strains (A) or IE-LACK transgenic mice and their negative littermates on the indicated background (B) were infected (solid bars) or not (empty bars) with 10⁷ L. major promastigotes. RNA was extracted from the draining LN 20 h after infection, and the relative levels of IL-4 mRNA were determined by semiquantitative reverse transcription-PCR. Data are means for two individual mice per group and are expressed in arbitrary units. Data are representative of three different experiments.

FIG. 2

Phenotype of LACK- and GP63-reactive T cells in infected mice. CD4⁺ T cells from the draining LN of BALB/c and B10.D2 mice were prepared 6 days after infection and incubated for 48 h without antigen (none) or with an optimal concentration of the indicated peptides. Cytokine contents were measured by enzyme-linked immunosorbent assay. Results from a representative experiment (of three) are shown. When cells from naive BALB/c or B10.D2 mice were incubated with LACK or GP63 peptides, the cytokine contents were below the limits of detection (1.4, 0.5, and 0.8 U of IFN-γ, IL-4, and IL-5, respectively, per ml).

FIG. 3

LACK-reactive T cells express a Th2 phenotype and are detrimental to the host in both BALB/c and B10.D2 mice. IE-LACK transgenic mice and their negative littermates on a B10.D2 background were inoculated with 2 × 10⁶ stationary-phase L. major promastigotes. (A) Lesion development in IE-LACK transgenic mice (filled symbols) and their negative littermates (empty symbols). Each data point represents the mean lesion size for 10 mice ± standard deviation. (B) Parasite burden in the tissues of IE-LACK transgenic mice (solid bars) and of their negative littermates (empty bars) 5 weeks after infection. (C) Frequencies of cytokine-secreting cells in IE-LACK transgenic mice and in their negative littermates. CD4⁺ T cells were prepared from the draining LN of the indicated mice 10 days after infection. Cells were incubated for 72 h with syngeneic antigen-presenting cells and an optimal concentration of SLA. Live cells were recovered, and the numbers of cells secreting IL-4 (filled bars), IFN-γ (empty bars), and IL-5 (hatched bars) were measured by an ELISPOT assay. The number of cytokine-producing cells detected when cells from B10.D2 naive mice were incubated with SLA was below 20/10⁶ cells.