Key Points Innate lymphoid cells (ILCs) and natural killer (NK) cells are components of the innate immune system that protect against invading pathogens. ILCs and NK cells contribute to immune…

Key Points Mast cells arise in the bone marrow, circulate as immature precursors, and develop into functional mast cells after entering peripheral tissues. The phenotype of mast cells is diverse,…

Key Points Fibroblasts are programmed epigenetically to determine the unique structure and function of different organs and tissues. These unique features might contribute to organ-specific disease. Tissue fibroblasts may be…

Key Points Immunoglobulins (Igs) are key to B cell function because they serve as both an antigen receptor and a major secreted product. The variable region binds antigen and is…

Key Points T cells develop primarily in the thymus. The importance of the thymus is underscored by the absence of T cells in patients in whom the thymus has failed…

Key Points Neutrophils are myeloid-lineage cells characterized by the presence of granules containing enzymes and other potentially toxic agents involved in host defense. Neutrophils are short-lived, terminally differentiated cells that…

Key Points At least two populations of tissue macrophages exist: tissue-resident cells that are embryonically derived and a monocyte-derived population. Their functions may be discrete. Macrophages are plastic and will…

Key Points Dendritic cells (DCs) together with monocytes and macrophages compose the mononuclear phagocyte system (MPS). DCs are professional antigen-presenting cells (APCs), abundant at body surfaces and within tissues, where…

Key Points Proteinases are generally classified into aspartic proteinases, cysteine proteinases, serine proteinases, and metalloproteinases according to their catalytic mechanism. Because of the optimal acidic pH and intra-cellular localization within…

Key Points Tissue repair and regeneration are partially determined by genetic factors. Successful regeneration requires a balanced immune cell response. The increased understanding of molecular signals governing native joint-resident stem…