Muscle specific tyrosine kinase-fluorophore conjugate compositions, kits and methods of using

A method for diagnosing muscle specific tyrosine kinase autoimmune myasthenia gravis in an individual, comprising the steps of:

• obtaining a sample comprising B cells from said individual and from a healthy control individual;
• contacting the individual sample and the healthy control sample with a conjugate comprising an extracellular domain of muscle specific tyrosine kinase comprising SEQ ID NO:
• 1 coupled to a fluorophore;
• contacting the individual sample and the healthy control sample with an antibody that binds B cells and
• measuring the levels of said muscle specific tyrosine kinase and said antibody that bind to the B cells from said individual sample and from said healthy control sample, wherein an increase in the binding levels in the individual sample compared to the binding levels in the healthy control indicates increased muscle specific tyrosine kinase specific B cells that produces pathogenic muscle specific tyrosine kinase antibodies for muscle specific tyrosine kinase myasthenia gravis.