Changes Of Activated T Cells In BALF From Children With Mycoplasma Pneumoniae Pneumonia

Background:Incidence of Mycoplasma pneumoniae pneumonia(MPP) keeps inceasing in recent years.It accounts about 20%-40%of all kind of pneumonia in children,accompanied by various kind of extra-pulmonary complications.However,the pathogenesis of the MPP is still under known clearly.There have been some kinds of proposed theories,including cellular adherence lesion and immunologic lesion mechanism.Especially,the later is the hot spot of the recent studies.So far there are a great quantity of reports about the blood and sputum focused on the immune mechanism but rarely about the bronchoalveolar lavage fluid(BALF).The results were contradictory.BALF comes from the illed bronchopulmonary tissue,so it may reflect the pathological changes of the respiratory system more directly and accurately than either blood or sputum.During the cytoimmunity process,T-lymphocytes act as an important role.Once the antigen is presented by the antigen-presenting cell(APC),T-lymphocytes(T cells) will be activated and induced to proliferation after antigen is combined with the antigen receptors on the surface of the T cells.Then many kinds of cytokines are secreted to activate macrophages and B cells followed by a series of immune response.So,a study on the changes of activated T cells and cytokines such as IL-6,IL-10 in BALF will be helpful for the immunologic lesion mechanism of MP infection.Objectives:The aim of this study was to investigate the expression levels of membrane molecules including CD₃⁺CD₆₉⁺,CD₃⁺HLA-DR⁺ and CD₃⁺CD₂₅⁺ on activated T cell subset and the levels of cytokines in BALF from children with MPP.Methods:BALF were collected by bronchoalveolar lavage(BAL) from 33 patients with MPP (MPP group),15 patients with non-MP infected pneumonia(nMPP group) and 10 children as control group without pulmonary infectious disease.The ratio of T cell and expression levels of CD₃⁺CD₆₉⁺,CD₃⁺HLA-DR⁺ or CD₃⁺CD₂₅⁺ on activated T cell subsets in BALF were determined by flow cytometry(FCM).IL-6 and IL-10 were determined by enzyme linked immunosorbent assay(ELISA).Results:1.Compared with non-MPP or control,the ratio of T cells was significantly decreased,but the expression levels of CD₃⁺CD₆₉⁺,CD₃⁺CD₂₅⁺ and CD₃⁺HLA-DR⁺ on activated T cell subsets were highly regulated in BALF from children with MPP(all P＜0.01).Compared with nMPP,the percentage of macrophages in total cells was significant higher in BALF from children with MPP(P＜0.05),there was no significant difference between MPP and control.The percentage of neutrophil in MPP group was significant lower than nMPP(P＜0.01) and higher than control(P＜0.05).The percentage of lymphocyte in MPP was significant lower than both nMPP or control(both P＜0.05). The percentage of eosinophil in MPP,nMPP and control gpoup showed no significant difference.Compared with control,the levels of IL-6 and IL-10 in MPP were signifcant higher(P＜0.01),while there was no significant difference between MPP and nMPP.2.There were 13 cases in MPP who had a chance to compare between acute stage and recovery stage.Compared with acute stage,the ratio of CD₃⁺T cells in recovery stage was significantly higher(P＜0.01),and a significant decrease in the percentage of CD₃⁺CD₆₉⁺(P＜0.01) and CD₃⁺CD₂₅⁺(P＜0.05).There was no significant difference on the expression level of CD₃⁺HLA-DR⁺ between acute stage and recovery stage.The percentage of lymphocyte in total cells was significantly increased in BALF at recovery stage after treatment(P＜0.01) while no significant difference for macrophages, neutrophil and eosinophil.The level of IL-6 was significantly decreased at recovery stage(P＜0.01).There was no significant difference on the level of IL-10 after treatment.3.Compared with the mild MPP,the expression level of CD₃⁺CD₂₅⁺ on activated T cell subsets,the levels of IL-6 or IL-10 were significantly increased in BALF in children with severe MPP(P＜0.01,0.05 or 0.05).There were no significant differences on the ratio of CD₃⁺T cells and the expression levels of CD₃⁺CD₆₉⁺ or CD₃⁺HLA-DR⁺ between the mild and serious MPP.The cytology counting of macrophages,neutrophil, eosinophil and lymphocyte between mild and serious group showed no significant differences.Conclusion:1.MP infection could induce the disfunction of T cell subsets,particularly the increased activation of T cell subsets,may play a major role in the inflammatory response in refractory MPP.2.The increased activation of T cell subsets may be related to the severity or prognosis of MPP.3.The the decreased ratio of lymphocytes in BALF in children with MPP showed that immune suppression may be involved in the mechanism of MPP.4.The levels of IL-6 or IL-10 may be related to the severity or prognosis of MPP.