SummaryModulation and suppression of the immune response of the host by nematode parasites have been reported extensively and the cysteine protease inhibitor (CPI or cystatin) is identified as one of the major immunomodulators. In the present study, we cloned and produced recombinant CPI protein from the murine nematode parasite Heligmosomoides polygyrus (rHp-CPI) and investigated its immunomodulatory effects on dendritic cell (DC) function and immune responses in mice. Bone-marrow-derived CD11c + DC (BMDC) that were exposed to rHp-CPI during the differentiation stage showed reduced MHC-II molecule expression compared with BMDC that were generated in normal culture conditions. The BMDC generated in the presence of rHp-CPI also exhibited reduced expression of CD40, CD86 and MHC-II molecules and reduced interleukin-6 and tumour necrosis factor-a cytokine production when stimulated with Tolllike receptor ligand CpG. Activation of BMDC generated in normal conditions induced by lipopolysaccharide and CpG was also suppressed by rHp-CPI, as shown by reduced co-stimulatory molecule expression and cytokine production. Furthermore, BMDC treated with rHp-CPI before ovalbumin (OVA) antigen pulsing induced a weaker proliferation response and less interferon-c production of OVA-specific CD4 + T cells compared with BMDC without rHp-CPI pre-treatment. Adoptive transfer of rHp-CPI-treated and OVA-loaded BMDC to mice induced significantly lower levels of antigen-specific antibody response than the BMDC loaded with antigen alone. These results demonstrated that the CPI from nematode parasites is able to modulate differentiation and activation stages of BMDC. It also interferes with antigen and MHC-II molecule processing and Toll-like receptor signalling pathway, resulting in functionally deficient DC that induce a suboptimum immune response.

IntroductionMalaria caused by infection with protozoan parasites of Plasmodium spp. is one of the most serious infectious diseases of humans and causes about one million deaths annually. Plasmodium infection may induce multiple disease syndromes including severe anemia, metabolic acidosis, and neurological dysfunction, e.g. cerebral malaria (CM) [1]. Sequestration of the Correspondence: Dr. Zhong Su e-mail: su_zhong@gibh.ac.cn parasitized red blood cells (pRBCs) in brain microvessels is a characteristic histopathology feature observed in human and murine CM and is believed to be the primary cause of the neurological syndrome [2,3]. Evidence from more recent studies supports the notion that CM is an immune-driven pathology. The proinflammatory cytokines and mediators produced in the "cytokine storm" during malaria induce activation and recruitment of cytotoxic CD8 + cells in brain blood vessels and upregulate the expression of adhesion receptors by brain endothelial cells, leading to leukocyte accumulation and capillary obstruction, cerebral hemorrhage, and hypoxia in brain tissues [1,[4][5][6]. Therefore, the immune regulatory cells and cytokines may be critical in counteracting the inflammatory response and prevention of malaria-associated www.eji-journal.eu 2908 Yunfeng Liu et al. Eur. J. Immunol. 2013. 43: 2907-2918 neuropathology. The levels of anti-inflammatory cytokines such as IL-10 and TGF-β have been shown to be inversely associated with the occurrence of CM in murine malaria [7,8]. However, no consensus has been reached concerning the role of regulatory T (Treg) cells in regulation of CM pathogenesis [9][10][11].B cells have been traditionally considered antibody-producing cell and APC. Many studies in recent years showed the existence of a subset of B cells that exhibit the immune regulatory functions (reviewed in [12]). An early study by Fillatreau et al.[13] reported a subset of B cells that produce IL-10 and inhibit the immune pathology in murine EAE. Further studies revealed that these regulatory B (Breg) cells play important roles in control of immunopathology in autoimmune diseases [14], cancer [15], and organ transplantation [16]. Breg cells have also been shown to modulate immune responses and immunopathology in infectious diseases. Protective immunities against Salmonella typhimurium and Brucella abortus infections were inhibited by transfer of Breg cells in mouse models [17,18]. Transfer of CD1d + CD5 hi Breg cells rendered the BALB/c mice more susceptible to Leishmania major infection [19]. Adoptive transfer of IL-10-producing B cells isolated from helminth-infected mice inhibited the allergic responses and autoimmune inflammation in recipient mice [20]. Thus, Breg cells are an important component of immunoregulatory system and plays critical roles in immune homeostasis.The immunomodulatory roles of Breg cells have been studied in autoimmune and infectious disease settings, but little is known of its role in regulation of immune response and immunopathology of malaria. In this study, we i...