Abstract: The present invention provides a therapeutic agent for progressive disease caused by an increase in Eomes-positive CD4-positive T cells, comprising a compound represented by formula (I) or a salt thereof as an active ingredient. In the formula, R1 is an aldopyranose residue, R2 is a hydrogen atom or a hydroxy group, R3 is —CH2—, —CH(OH)—CH2—, or —CH?CH—, R4 is a hydrogen atom or CH3, x is 0 to 35, and y and z each are an integer satisfying y+z=0 to 3.

Abstract: A method for diagnosing myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is provided in the present disclosure. The present disclosure provides a method that uses the B cell receptor (BCR) repertoire as an indicator of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). One or more variables selected from the group consisting of the frequency of use of one or more genes in the IgGH heavy chain variable region of the BCR in a subject, the BCR diversity index in a subject, and the level of one or more immune cell subpopulations in a subject can be used as an indicator of ME/CFS in the subject.