Abstract: 　Objective　To explore the immune status and clinical characteristics of herpes virus antibody positive Mycoplasma pneumoniae pneumonia (MPP). Method　The clinical data of 360 children aged 2 months to 16 years hospitalized with MPP from January 2015 to May 2017 were retrospectively analyzed. A total of 162 children with positive antibody to epsteinbarr virus (EBV), cytomegalovirus (CMV) or herpes simplex virus (HSV) were selected as the antibody positive group. Meanwhile, 198 children with negative EBV, CMV, and HSV antibodies hospitalized in the same period were enrolled in the control group. And the analysis and comparison were performed. Results　In 360 children (188 boys and 172 girls) with MPP, 162 children were positive for herpes virus IgM antibody, among whom 97 children (26.9%) were positive for EBV IgM, 39 children (10.8%) were positive for CMV IgM, and 97 children (26.9%) were positive for HSV IgM. All the children were not given antiviral treatment, and the symptoms were relieved after the treatment. The proportions of severe MPP, lobar-like consolidation and respiratory failure in antibody positive group was higher than those in control group (P<0.05). The levels of serum IgM, CD4+T cells, CD8+T cells, lymphocytes, NK cells, WBC, Lactate dehydrogenase (LDH) and alanine aminotransferase (ALT) were all higher than those in control group (P<0.05). The duration of macrolide antibiotics were longer than those in control group and the rate of hormone use was higher than that of control group (P<0.05). In MPP children with two positive IgM antibodies, the serum IgM and triglyceride levels were higher than those with one positive IgM antibody, and the difference was statistically significant (P<0.05). Compared with MPP children with one positive IgM antibody, those with three positive IgM antibodies had longer hospital stay, longer fever time and longer duration of macrolides antibiotics treatment, higher levels of IgM and ALT, and higher incidence of severe MPP, and differences were statistically significant (P<0.05). Conclusions　MPP children with positive IgM to herpes virus have strong inflammatory response, severe clinical symptoms, long course of disease and many complications, and thus need longer treatment.

Key words: Mycoplasma pneumoniae pneumonia;　IgM of virus;　immune disorder;　clinical characteristic