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Target-induced anergy of natural killer cytotoxic function is restricted to the NK-target conjugate subset
1Department of Microbiology and Immunology, University of California at Los Angeles School of Medicine.
Abstract:
This study examined the characteristics of functional anergy of natural killer cells (NK) following their interaction with target cells. Purified NK cells were cocultured with K562 for 15 min or 4 hr to allow for binding of targets to NK cells. The resulting NK-target conjugates were then dissociated by EDTA, and the unbound NK cells were separated from the targets by flow cytometry and cell sorting. Compared to untreated NK cells, the K562-dissociated NK cells were inhibited for cytotoxic function as assessed by the 51Cr release assay and by the single killer frequency assay and also responded poorly following activation by IL-2 or IFN-alpha. The inactivated NK cells had a diminished ability to reform conjugates with the target cells. Following cell sorting of the NK subsets, the conjugate subset had the least cytotoxic activity when compared to both the free NK subset or the unfractionated NK population. The IL-2 response observed with the unfractionated anergic NK cells was found to be due to the activation of the NK free cell subset while the conjugate subset was poorly responsive to IL-2. The cell surface CD16, CD2, and CD56 antigen expression was downmodulated in the conjugate subset but not in the free cells. However, the CD69 surface expression was significantly upregulated on the surface of the NK conjugate subset and was potentiated following treatment with IFN-alpha and IL-2. These results demonstrate that target-mediated anergy of NK cells is restricted to the NK-target conjugate subset while sparing the remaining free cell subset. Further, the findings demonstrate that the anergic NK cells express the phenotype CD16dimCD2dimCD56dimCD69brightCD11bbright.
Insights
Target cell interaction induces functional anergy in natural killer (NK) cells, specifically within the NK-target conjugate subset. This anergy impairs cytotoxic function and cytokine response, characterized by specific cell surface marker changes.
Area of Science:
- Immunology
- Cell Biology
Background:
- Natural killer (NK) cells are crucial for innate immunity, mediating cytotoxicity against target cells.
- NK cell function can be modulated by interactions with target cells, potentially leading to functional inactivation or anergy.
Purpose of the Study:
- To investigate the characteristics of functional anergy in NK cells after interaction with target cells.
- To identify the specific NK cell subset responsible for target-mediated anergy.
- To elucidate the phenotypic changes associated with NK cell anergy.
Main Methods:
- NK cells were co-cultured with K562 target cells.
- NK-target conjugates were dissociated, and NK cell subsets (conjugate and free) were isolated using flow cytometry and cell sorting.
- Cytotoxic function was assessed using 51Cr release and single killer frequency assays.
- Cytokine (IL-2, IFN-alpha) responsiveness and cell surface antigen expression (CD16, CD2, CD56, CD69, CD11b) were analyzed.
Main Results:
- NK cells from K562-dissociated conjugates exhibited inhibited cytotoxic function and poor response to IL-2 or IFN-alpha compared to untreated NK cells.
- The NK-target conjugate subset showed significantly lower cytotoxic activity than the free NK cell subset.
- Anergic NK cells in the conjugate subset displayed downmodulation of CD16, CD2, and CD56, with upregulation of CD69 and CD11b.
- The functional unresponsiveness was specific to the NK-target conjugate subset, while the free NK cell subset remained responsive.
Conclusions:
- Target-mediated anergy in NK cells is restricted to the NK-target conjugate subset.
- Anergic NK cells exhibit a distinct phenotype: CD16dimCD2dimCD56dimCD69brightCD11bbright.
- This study identifies a specific mechanism of NK cell functional inactivation following target cell engagement.