**1. Introduction**

Sjögren's syndrome (SS) is the second most common autoimmune disorder after rheumatoid arthritis (RA) [1]. Like systemic lupus erythematosus (SLE), SS is a chronic and systemic autoimmune disease [2]. While SS is most commonly associated with xerostomia, xeropthalmia, and lymphocytic infiltration into the exocrine glands, SS patients may present with gastrointestinal symptoms, fatigue, pulmonary problems, and experience a higher incidence of non-Hodgkin's B cell lymphoma (NHL) [2,3]. The lymphocytes that infiltrate into the exocrine glands can organize into focal structures in which germinal center-like formation is present in approximately 25% of primary SS patients [4], establishing a structure for local production of autoantibodies [4,5]. SS primarily affects women and features a highly skewed sex distribution (9:1) [6]. SS is a complex heterogenous disease that can present alone, referred to as primary SS (pSS), or as secondary SS with another autoimmune disease such as RA or SLE. While the adaptive immune cells like B and T cells have traditionally attracted the most interest due to their predominant presence in the exocrine glands and the immunological importance autoantibodies, increasing evidence shows that immune system dysfunction in SS incorporates cells of the innate immune system as well [7–12]. In this review, we aim to present the current state of knowledge on

how the common cell types of the innate and adaptive immune systems contribute to SS as revealed by studies of human patients and animal models.
