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CD45-negative mutants of a rat natural killer cell line fail to lyse tumor target cells
G M Bell1, G M Dethloff, J B Imboden
1Department of Medicine, San Francisco VA Medical Center, CA.
Abstract:
To examine the role of CD45 in NK cell activation, we isolated three mutants and one variant of a rat NK cell line, RNK-16. Each of these lacked cell-surface expression of CD45 and did not have detectable transcripts for CD45 on Northern blot analysis. The CD45-negative cells expressed CD2, CD53, and NKR-P1, but mAb-induced perturbations of these molecules did not induce protein tyrosine phosphorylations and increases in the concentration of cytoplasmic-free calcium, as occurred in the wild-type RNK-16. Unlike the wild-type cells, the CD45-negative cells failed to lyse YAC-1 and RL-male-1 tumor targets. The cytolytic activity of the CD45-negative cells could be stimulated pharmacologically by ionomycin and PMA, which, when added to the cytotoxicity assays, induced killing of tumor targets. These studies suggest that CD45 is required for the response of RNK-16 cells to target cells and for signaling through CD2, CD53, and NKR-P1.
Insights
CD45 is essential for natural killer (NK) cell activation and tumor cell lysis. Without CD45, NK cells cannot signal properly or kill target cells, highlighting its critical role in immune responses.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Natural killer (NK) cells are crucial immune cells involved in tumor surveillance and elimination.
- CD45, a protein tyrosine phosphatase, plays a regulatory role in immune cell signaling.
- The specific function of CD45 in NK cell activation and cytotoxicity remains to be fully elucidated.
Purpose of the Study:
- To investigate the role of CD45 in the activation and cytotoxic function of rat NK cell line (RNK-16).
- To determine if CD45 is required for signal transduction pathways initiated by NK cell surface receptors.
Main Methods:
- Isolation and characterization of CD45-negative RNK-16 cell mutants.
- Analysis of cell surface marker expression (CD2, CD53, NKR-P1) using flow cytometry.
- Assessment of protein tyrosine phosphorylation and intracellular calcium mobilization upon receptor stimulation.
- Evaluation of cytotoxic activity against tumor target cells (YAC-1, RL-male-1).
- Pharmacological stimulation of cytotoxicity using ionomycin and PMA.
Main Results:
- CD45-negative RNK-16 cells expressed CD2, CD53, and NKR-P1 but failed to undergo downstream signaling (tyrosine phosphorylation, calcium flux) upon stimulation of these receptors.
- CD45-negative cells exhibited significantly reduced or absent lysis of tumor targets compared to wild-type RNK-16 cells.
- Pharmacological activation with ionomycin and PMA restored the cytolytic activity of CD45-negative cells.
Conclusions:
- CD45 is indispensable for RNK-16 cell activation and cytotoxic response against tumor cells.
- CD45 is required for signal transduction mediated by NK cell receptors such as CD2, CD53, and NKR-P1.
- These findings underscore the critical role of CD45 in NK cell-mediated immunity and anti-tumor activity.