Abstract
Cytokines have the potential to drastically augment immune cell activity. Apart from altering the expression of a multitude of proteins, cytokines also affect immune cell dynamics. However, how cytokines affect the molecular dynamics within the cell membrane of immune cells has not been addressed previously. Molecular movement is a vital component of all biological processes, and the rate of motion is, thus, an inherent determining factor for the pace of such processes. Natural killer (NK) cells are cytotoxic lymphocytes, which belong to the innate immune system. By fluorescence correlation spectroscopy, we investigated the influence of cytokine stimulation on the membrane density and molecular dynamics of the inhibitory receptor Ly49A and its ligand, the major histocompatibility complex class I allele H-2Dd, in freshly isolated murine NK cells. H-2Dd was densely expressed and diffused slowly in resting NK cells. Ly49A was expressed at a lower density and diffused faster. The diffusion rate in resting cells was not altered by disrupting the actin cytoskeleton. A short-term stimulation with interleukin-2 or interferon-α + β did not change the surface density of moving H-2Dd or Ly49A, despite a slight upregulation at the cellular level of H-2Dd by interferon-α + β, and of Ly49A by IL-2. However, the molecular diffusion rates of both H-2Dd and Ly49A increased significantly. A multivariate analysis revealed that the increased diffusion was especially marked in a subpopulation of NK cells, where the diffusion rate was increased around fourfold compared to resting NK cells. After IL-2 stimulation, this subpopulation of NK cells also displayed lower density of Ly49A and higher brightness per entity, indicating that Ly49A may homo-cluster to a larger extent in these cells. A faster diffusion of inhibitory receptors could enable a faster accumulation of these molecules at the immune synapse with a target cell, eventually leading to a more efficient NK cell response. It has previously been assumed that cytokines regulate immune cells primarily via alterations of protein expression levels or posttranslational modifications. These findings suggest that cytokines may also modulate immune cell efficiency by increasing the molecular dynamics early on in the response.
Highlights
Natural killer cells play an essential role in innate immunity and protect the host against viral infection and tumors [1]
We investigated the influence of cytokine stimulation on the major histocompatibility complex (MHC) class I and Ly49 membrane dynamics and density using fluorescence correlation spectroscopy (FCS) [20]
We identified a subpopulation of Natural killer (NK) cells that exhibited a fast diffusion rate of both the inhibitory receptor Ly49A and of the MHC class I molecule H-2Dd upon cytokine stimulation
Summary
Natural killer cells play an essential role in innate immunity and protect the host against viral infection and tumors [1]. Murine NK cells express a family of inhibitory receptors called Ly49 receptors, which have major histocompatibility complex (MHC) class I molecules as ligands. MHC class I is expressed by virtually all healthy cells, but can be downmodulated upon infection or in tumorigenesis. In the absence of sufficient cognate MHC class I expression, NK cells proceed to kill the target cells due to lack of signaling through their inhibitory receptors, a process called missing-self recognition [2]. Cytokines are important modulators of NK cell activity. Type I interferons, such as interferon alpha and beta (IFN-α + β), are strong inducers of NK cell cytotoxicity, primarily during viral infections [9, 10]. Type I interferons, in addition, strongly upregulate MHC class I on many cell types, including lymphocytes [11, 12]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have