Relationship between CD107a expression and cytotoxic activity
Introduction
Natural killer (NK) cells are a subset of large granular lymphocytes defined by the absence of T cell receptor (CD3) and by the surface expression of CD56 [1] and comprise 5–15% of lymphocytes in peripheral blood [2]. These cells play an important role in innate immunity as they are characterized by their strong cytolytic responses against tumors or virus-infected cells and by their ability to release cytokines and chemokines mediating inflammatory responses to induce hematopoiesis and modulating subsequent adaptive immune responses [3].
NK cells contain high concentrations of (pre-formed) cytotoxic granules in their cytoplasm as they circulate in the periphery [1], and such granules are pre-formed during NK cell development and maturation. Upon target cell recognition and conjugation, the granules are actively directed to the site of cell–cell contact. The lytic lysosomes fuse with the plasma membrane and secrete soluble effector molecules into the forming cytotoxic immunological synapse. At the same time, several transmembrane components of the granules containing perforin and granzymes are exposed on the cell surface and dictate the fate of effector and target cells [4], [5]. We and others recently showed that NK cells can differentiate into cells with NK1 and NK2 phenotypes, are able to produce type 1 and type 2 cytokines and also may display regulatory functions in humans [6], [7], [8]. The production of cytokines such as interferon (IFN)-γ and tumor necrosis factor (TNF)-α further enhances their cytotoxicity and modulates the innate and adaptive immune systems, directing immune responses towards Th1 phenotype [9].
As degranulation occurs, secretory lysosomes are released, and the lysosome-associated membrane protein-1 (LAMP-1, CD107a) is transported to the surface of NK cell rendering it accessible for antibody binding, thus making it possible to identify NK cells which have been activated for degranulation [10]. There are several methods for estimating the cytotoxic activity of NK cells; lysis of the 5-(and-6-)-carboxyfluorescein succinidimyl ester (CFSE)-labeled K562 cells is a good method for the determination of NK-mediated lytic capacity. In this study, the expression of CD107a is compared with lysis of K562 cells and the relationship between the expression of CD107a, cytokine secretion and cytotoxic activity in NK cells and lymphocyte population to various stimuli has been determined. According to our findings, CD107a expression seems to be a good candidate marker for the cytotoxic activity of NK cells.
Section snippets
Study group
A total of 21 healthy individuals (10 women and 11 men, mean age; 30 ± 3) were enrolled to the study. An approval of Local Ethical Committee in compliance with declaration of Helsinki and informed consent of healthy subjects were taken.
Target cell population
Human leukemia K562 cell line, target of NK cell lytic activity because of the lack of major histocompatibility complex (MHC) class I molecule expression, were obtained from the American Type Culture Collection (ATCC; Manassas, VA). K562 cells were cultured in
IL-2 stimulates CD107a expression on NK and cytotoxic T cells
It is well known that IL-2 activates NK cells providing an important component for the destruction of tumor cells. To explore the effect of IL-2 and IL-10 on CD107a expression, isolated PBMCs were co-cultured with K562 cells in the presence of IL-2, IL-10 and PMA/Ionomycin (PMA/I). Expression of CD107a on lymphocytes, CD8+ T and CD56+ NK cells were evaluated by flow cytometry. IL-2 and PMA/I stimulation significantly increased CD107a expression in lymphocytes (p < 0.001 and p < 0.05, respectively)
Discussion
NK cells have distinct morphologic, phenotypic and functional properties compared to T and B cells, are responsible for immune surveillance and represent one of the major components of innate immunity [12]. Functionally they are important source of immunoregulatory cytokines and can interact with other immune cells to trigger adaptive or antigen specific immune responses [13]. NK cells are regulated by inhibitory and activatory receptors to protect normal “self” but eliminate “dangerous”
Acknowledgments
This work was supported by the Research Fund of The University of Istanbul and we thank Prof. Dr. Cezmi Akdis from Swiss Institute of Allergy and Asthma Research (SIAF) for his kind collaboration.
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