Modulation of B-lymphocyte and NK cell activities by glycoinositolphospholipid purified from Trypanosoma cruzi

Abstract

Glycoinositolphospholipids (GIPLs) are some of the major glycolipids of the Trypanosoma cruzi surface that were previously shown to activate B cells. In the present study, we investigated whether (i) T. cruzi GIPLs could induce immunoglobulin secretion from B cells in the absence of T cells and NK cells and whether (ii) NK cells are also stimulated by the GIPLs. B cells purified from mice deficient in both T and NK cells (CD3epsilon transgenic mice) secreted immunoglobulin in response to the GIPL. This response was increased by coculture with a murine NK cell line. The T. cruzi GIPL also increased the NK cell (interleukin-2 induced) proliferative response. Our data indicate that the T. cruzi GIPL has a direct stimulatory effect on NK cells and induces immunoglobulin secretion in the absence of T lymphocytes and NK cells. These findings suggest that this T. cruzi-derived molecule may be one of the stimulators that lead to NK cell activation during T. cruzi infection.

FIG. 1

Enhancement of the GIPL-stimulated IgM secretion in the presence of an NK cell line. Splenic B cells were purified from CD3ɛ tg mice and used at 10⁵/ml. Some cultures were stimulated with T. cruzi GIPL (added at 1.5 μM) and IL-2 (50 U/ml) either alone or in combination. The PKO NK cell line (400 cells/ml) was added where indicated. The dextran-conjugated anti-delta antibody (AF3-dextran) was added at 20 ng/ml. Culture supernatants were obtained from triplicate cultures after 7 days, and IgM levels were determined by ELISA. The results are representative of three independent experiments.

FIG. 2

Proliferation of the PKO NK cell line in the presence of cytokines and T. cruzi-derived glycoconjugates. Cells of the PKO NK line (1.25 × 10⁵/ml) were stimulated with the indicated glycoconjugates. GIPL purified from T. cruzi was used at 15 μM. This was observed to be the most effective dose in titration studies (data not shown). The indicated doses (micromolar) of the PIns-oligosaccharide were also added. IL-2 was added at 50 U/ml, and IL-12 was added at 0.2 ng/ml. Tritiated thymidine incorporation was measured after a 48-h culture. Cultures performed in the absence of IL-2 showed thymidine incorporation below 300 cpm irrespective of the stimulus used. Asterisks indicate statistically significant differences at a P value of ≤0.005.