| Background & Objectives: Psoriasis is a kind of skin disease with unclear causes, which can be triggered by many factors. It's widely acknowledged guttate psoriasis is a T-cell mediated inflammatory skin disease which has been associated with group A, (3 haemolytic streptococcal infections. There is hypothesis that streptococcal M6 protein, as a germ superantigen, play an key role in the pathogenesis of psoriasis. Superantigens belong to a family of immunoglobulin proteins which greatly stimulate the proliferation potential of T-cells. Study shows that streptococcal M6-protein share high ammal acid sequence homology with 50 kDa type-I human epidermal keratin. The consensus sequences mainly include highly repeated 7-peptide sequences which comprise of α-helical structure. In former studies, β-haemolytic streptococci were separated from throat infection isolates of psoriasis patients. They were cultured and the M6-protein were purified. It wasfound that the titer of antibodies to M6-protein was apparently higher in serum of guttate psoriasis patients than plaque psoriasis patients and normal group, preliminarily proving the close association between streptococcal M6 protein and guttate psoriasis patients. The purpose of this paper is to further explore if there is a mechanism of group A, β-type streptococcal M6 protein as superantigen in the pathogenesis of guttate psoriasis. Methods:we applied purified M6 protein to stimulate peripheral blood mononuclear cells(PBMC) from guttate psoriasis patients, observing PBMC's proliferation response to trace M6-protein (100ng).Comparation was done to plaque psoriasis and normal group, with staphylococcal enterotoxin (SEB) as superantigen which is widely recognized, and tetanus toxin (TT) as ordinary antigen, PRMI-1640 as negative control. Detail methods were as follows: during May 2001 to June 2002, totally 30 confirmed guttate psoriatic patients and 30 normal controls, were selected, 4mL venous blood were extracted from each of the above individual. PBMCs were seperated by means of density gradient centrifugal method, and 1 × 109 /L cells were suspended inRPMI-1640 culture medium. Each 100uL of cell suspension was added into each well of 40-well plate. Then lOOuL of each of the following reagents (1mg/L for all): M6-protein ,SEB,TT,RPMI-1640 was added into each well respectively and cultivated at 37℃, 5% CO2, saturated relative humidity for 6d. 4 hours before culturing ending, 20uL MTT was added to each of the well. After culturing, 150uL of formazan was further added (to each well) . A microplate reader was employed to measure the absorbance of light with doubwave lengthes (570nm , 455nm) . Observations were made on the proliferation changes among 20 guttate psoriatic patients at different concentration (1mg/L, 2mg/L, 4mg/L, 8mg/L) of M6 and SEB.To further study the mechanism of PBMC proliferation in response to M6-protein in psoriasis, we tested the concentration change of IFN-γ and IL-4 in supernant of PBMC from 20 guttate psoriatic patients after M6-protein stimulation. For guttate psriatic patients, 1mL of above supernatant, lOOuL of M6, RPMI-1640 was added to each well of a 24 -well plate respectively. 300uL of supernatant was collected after 72 hr cultivation. After centrifugation, the supernatant was freezed at -20℃for storage, or tested by ABC-ELISA.Results:long M6-protein resulted in significant proliferation of PBMC in guttate psoriasis patients, which was obvious higher than that of tetanus toxin(TT) and RPMI-1640 at same concentration(P<0.001); It was also observed there existed signigicant difference of PBMC proliferation in response to M6-protein among guttate psoriasis, plaque psoriasis and normal group (P<0.001); significant difference of PBMC proliferation in response to SEB among guttate psoriasis, plaque psoriasis and normal group; no difference of PBMC proliferation in response to varied concentration of M6-protein and SEB among guttate psoriasis. That showes very low concentration M6-protein results in significant P...
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