The present study was a single-center, prospective, non-comparative in which macrophage activation syndrome patients were selected as the main subjects to evaluate the effect and safety of Ruxolitinib and methylprednisolone regimens as the first-line therapy .

Inclusion Criteria:

1. Meet hemophagocytic lymphohistiocytosis (HLH)-04 diagnostic criteria; patients were diagnosed with autoimmune disease associated HLH (Macrophage activation syndrome, MAS).
2. No HLH induction therapy was performed.
3. The expected survival time is more than 1 month.
4. Serum creatinine ≤ 1.5 times normal；Serum human immunodeficiency virus(HIV) antigen or antibody negative； Hepatitis C virus (HCV) antibody is negative, or HCV antibody is positive, but HCV RNA is negative；HBV copies less than 1E+03 copies/ml.
5. Total bilirubin ≤10 times the upper limit of normal; serum creatinine ≤1.5 times the normal value
6. The left ventricular ejection fraction (LVEF) was normal.
7. No uncontrollable infection.
8. Contraception for both male or female.
9. Informed consent obtained.

Exclusion Criteria:

1. Pregnancy or lactating Women；
2. Allergic to ruxolitinib；
3. Active bleeding of the internal organs；
4. uncontrollable infection；
5. Serious mental illness;
6. Non-melanoma skin cancer history;
7. Patients unable to comply during the trial and/or follow-up phase;
8. Participate in other clinical research at the same time.