Objectives: Abnormalities and hyperactivation of B cells have been described in idiopathic inflammatory myopathies (IIM). However, little is known about changes in the homeostasis of peripheral blood B cells in adult IIM patients. The aim of this study was to identify phenotypic alterations of B cell subsets and their relation to the overall clinical profile.
Methods: Blood samples were collected from 25 adult IIM patients and 15 healthy controls. Peripheral B cell subsets were classified into non-switched memory B cells (CD19+CD27+lgD+), switched memory B cells (CD19+CD27+lgD-), double-negative (DN) memory B cells (CD19+CD27-lgD-) and naïve B cells (CD19+CD27-lgD+) based on their surface phenotype as measured by flow cytometry. The clinical profile of IIM and its correlation with B cell subsets was further evaluated.
Results: Frequencies of CD19+ B cells and naïve B cells were increased in adult IIM patients compared with healthy controls (p=0.005 and p<0.001, respectively) and the frequency of memory B cells was decreased (p<0.001). Moreover, patients with a rash had lower non-switched memory B cells proportion (p=0.032). Patients with anti-MDA5+ antibodies had higher CD19+ B cells proportion than anti-ARS+ patients (p=0.046). Patients who were not receiving treatment had elevated levels of CD19+ B cells and naïve B cells along with reduced non-switched memory B cells compared with patients who were receiving treatment (p=0.021, p=0.036 and p=0.032, respectively).
Conclusions: Our findings demonstrate abnormalities in the homeostasis of the B cell subsets present in adult IIM patients, characterised by expanded CD19+ B cells and naïve B cells but reduced memory B cells. Phenotypic abnormalities of B cell subsets are associated with the presence of a rash, with anti-MDA5 positivity and with treatment.