Boosting the suppressive effects of Ascaris suum components in IFN-γ-deficient mice Potencialização do efeito supressor de componentes do Ascaris suum em camundongos deficientes em IFN-γ

High molecular weight components from Ascaris suum extract suppress ovalbumin-specific immunity in mice. In IFN-γ-deficient mice, ovalbuminspecific delayed-type hypersensitivity reactions are more strongly downregulated by these suppressive components. Here, the cellularity of the delayed-type hypersensitivity reaction in IFN-γ-deficient mice and the increased downregulation induced by Ascaris suum components were analyzed. IL-12p40-dependent neutrophilic influx was predominant. Suboptimal doses of the suppressive fraction from this nematode completely inhibited the hypersensitivity reaction, thus indicating intensification of the immunosuppression under conditions of intense recruitment of IFN-γ-independent neutrophils. Key-words: Ascaris suum. Delayed-type hypersensitivity. Immunosuppression. IFN-γ-deficient mice. Neutrophil. RESUMO Componentes de alto peso molecular do extrato de Ascaris suum suprimem a imunidade específica à ovalbumina em camundongos. Em camundongos geneticamente deficientes de IFN-γ a reação de hipersensibilidade tardia específica para ovalbumina foi mais fortemente prejudicada por estes componentes supressivos. Aqui, a celularidade da reação de hipersensibilidade tardia em camundongos deficientes de IFN-γe o incremento na supressão induzida por componentes do Ascaris suum foram analisados. Influxo neutrofílico, dependente de IL-12p40, foi predominante. Dose subótima da fração supressiva do nematódeo inibiu completamente a reação de hipersensibilidade, indicando uma intensificação da imunossupressão em condições de recrutamento intenso de neutrófilos independente de IFN-γ.  Palavras-chaves: Ascaris suum. Hipersensibilidade tardia. Imunossupressão. Camundongos deficientes em IFN-γ. Neutrófilos. 1. Laboratory of Immunopathology Keizo Asami, Department of Pharmaceutical Sciences, Federal University of Pernambuco, Recife, PE, Brazil. 2. Department of Immunology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, SP, Brazil. Financial support: Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP). Address to: Dra. Valdênia M.O. Souza. Laboratório de Imunopatologia Keizo Asami/ UFPE. Av. Prof. Moraes Rego s/n, Cidade Universitária, 50670-901 Recife, PE, Brazil. Tel: 55 81 2101-2515; Fax: 55 81 2126-8485 e-mail: [email protected] Received in 19/11/2007 Accepted in 14/04/2009 Helminth infections inhibit the host’s protective Th1-type immune response to non-related pathogenic agents such as virus, parasites and bacterial antigens 4 . On the other hand, harmful Th1 or Th2 responses leading to autoimmune encephalomyelitis or enteric allergy, respectively, can be also controlled in the presence of helminth antigens . With regard to the nematode Ascaris suum, the regulatory mechanisms induced by its immunosuppressive components have been the focus of our studies for some time. These components correspond to the high molecular weight fraction, eluted in the first peak (PI), after gel filtration chromatography of the adult Ascaris suum body extract. In mice, when PI was combined with ovalbumin (OVA) and adjuvant, both OVA-specific Th1 and Th2 immune responses were found to be impaired (lymphoproliferation, delayed-type hypersensitivity (DTH) reactions, IgG2a/IgG1/IgE and IL-2/ IFN-γ/IL-4/IL-10 production). Using IL-4 or IL-10 knockout mice that were immunized in the same way, we demonstrated the essential role of IL-10 in suppressing the OVA-specific Th2 immune response, while IL-10 plus IL-4 were required for suppressing Th1-related parameters. In IL-12 or IFN-γ knockout mice, the PI suppressive ability remained intact. Unexpectedly, OVA-immunized IFN-γ-deficient mice developed a very intense OVA-specific DTH reaction, that seemed to be more strongly impaired when these mice received PI. Thus, in the present study, we investigated the type of infiltrating cell in an OVA-specific DTH and analyzed the intensity of the suppressive effect of PI in the absence of IFN-γ. For this, C57BL/6 mice that presented targeted disruption of the IFN-γ gene (IFN-γ-/-) and wild-type C57BL/6 mice were subcutaneously immunized with OVA (200μg of protein/animal; Sigma Chemical Co) or OVA (200μg of protein/animal) plus PI (200 or 50μg of protein/animal), emulsified in complete Freund’s adjuvant (Sigma Chemical Co), on the base of the tail (0.2ml/ animal). PI was obtained after gel filtration chromatography (XK 26/100 column of Sephacryl S-200; Pharmacia, Uppsala, Sweden) on adult Ascaris suum body extract and was concentrated with Centriprep 100 (Amicon, Beverly, MA, USA). After eight days, the mice were challenged in the hind footpad with 2%