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ABSTRACT
NK cells (Natural killer cells -NK)
comprise 10-15% of peripheral blood mononuclear cells and shows
morphology of large, granular lymphocytes (LGL). NK cells bind and
kill virus infected and malignantly transformed cells, without prior
sensitization. Apart from this, NK cells participate in hematopoiesis
regulation, reproduction processes, as well as in numerous immunology
activities in-vitro defance in the infection against micoplasm's
and fungy. NK cells originate from the bone marrow and numerous
studies confirm that peripheral blood lymphocytes with NK cell function,
have immunophenotypic characteristics: CD56+, CD16+, CD3-, TCR-,
surface Ig-.
NK cell activity was expressed by percentage of lysis tumor cells
(K-562, MOLT, and Daudi) previously labelled with radioactive 51Cr
or by the release of intracellular enzymes.
NK cells kill tumor cells by two mechanisms. The first cytotoxic
mechanism was spontaneous and major histocompatibile antigen independent
process, and the second mechanism was antibody dependent cellular
cytotoxicity (ADCC).
After the activation, NK cells release, from previously performed
granules, during the exocytosis process enzymes: perforin, serine
esterase (granzymes A and B) chondroitin sulphate, phospholypases
and other lytic molecules which kill tumor cells during the necrotic
process. However, NK cells in the non-secretory mechanism, kill
tumor cells by apoptosis form of cell death by superfamily of TNF
receptors. Apoptotic and necrotic forms of cell death sometimes
were like one process, but specific inhibitors of protein synthetase
enzymes (Ca/
Mg
dependent endonuclease) block apoptosis but not the necrotic form
of cell death, which gives possibility to analyze and evaluate these
two processes separately.
Keywords: NK cells, immunophenotype, activations, effector mechanisms, apoptosis, necrosis.
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