A Recombinant Fragment of Human Surfactant Protein D Suppresses Basophil Activation, Th2 and B Cell Responses in Grass Pollen-induced Allergic Inflammation

Abstract

Rationale: rfhSP-D has been shown to suppress house dust mite and Aspergillus 74 fumigatus-induced allergic inflammation in murine models. 75 Objectives: We sought to elucidate the effect of rfhSP-D on FcεRI and CD23- 76 mediated grass pollen induced allergic inflammatory responses. 77 Methods: rfhSP-D, containing homotrimeric neck and lectin domains, was 78 expressed in Escherichia coli BL21 (λDE3) pLysS. PBMCs and sera were obtained 79 from grass pollen allergic individuals (n=27). The effect of rfhSP-D on basophil 80 activation and histamine release was measured by flow cytometry. IgE-facilitated 81 allergen binding and presentation was assessed by flow cytometry. Th2 cytokines 82 were measured in cell culture supernatants. The effect of rfhSP-D on IgE production 83 by B cells when stimulated with CD40L, IL-4 and IL-21 was also determined. 84 Results: rfhSP-D bound to Phleum pratense in a dose- and calcium-dependent 85 manner. Allergen-induced basophil responsiveness and histamine release was 86 inhibited in the presence of rfhSP-D, as measured by CD63, CD203c 87 (P=0.0086,P=0.04205), and intracellular-labelled DAO (P=0.0003,P=0.0148). The 88 binding of allergen-IgE complexes to B cells was reduced by 51%(P=0.002) in the 89 presence of rfhSP-D. This decrease was concomitant with reduction in CD23 90 expression on B cells (P<0.001). rfhSP-D suppressed allergen-driven CD27- 91 CD4+CRTH2+ T cell proliferation (P<0.01), IL-4 and IL-5 levels (all, P<0.01). 92 Moreover, rfhSP-D inhibited CD40L/IL-4 and IL-21-mediated IgE production(77.12%; 93 P=0.02) by B cells. 94 Conclusion: For the first time, we show that rfhSP-D inhibited allergen-induced 95 basophil responses at a single cell, level and suppressed CD23-mediated facilitated 5 allergen presentation and Th2 cytokine production. 96 In addition, rfhSP-D inhibited IgE 97 synthesis by B cells, which is also a novel observation.