Abstract
Two populations of human natural killer (NK) cells can be identified in peripheral blood. The majority are CD3−CD56dim cells while the minority exhibits a CD3−CD56bright phenotype. In vitro evidence indicates that CD56bright cells are precursors of CD56dim cells, but in vivo evidence is lacking. Here, we studied NK cells from a patient that suffered from a melanoma and opportunistic fungal infection during childhood. The patient exhibited a stable phenotype characterized by a reduction in the frequency of peripheral blood CD3−CD56dim NK cells, accompanied by an overt increase in the frequency and absolute number of CD3−CD56bright cells. These NK cells exhibited similar expression of perforin, CD57 and CD158, the major activating receptors CD16, NKp46, NKG2D, DNAM-1, and 2B4, as well as the inhibitory receptor CD94/NKG2A, on both CD56bright and CD56dim NK cells as healthy controls. Also, both NK cell subpopulations produced IFN-γ upon stimulation with cytokines, and CD3−CD56dim NK cells degranulated in response to cytokines or K562 cells. However, upon stimulation with cytokines, a substantial fraction of CD56dim cells failed to up-regulate CD57 and CD158, showed a reduction in the percentage of CD16+ cells, and CD56bright cells did not down-regulate CD62L, suggesting that CD56dim cells could not acquire a terminally differentiated phenotype and that CD56bright cells exhibit a maturation defect that might result in a potential altered migration pattern. These observations, support the notion that NK cells of this patient display a maturation/activation defect that precludes the generation of mature NK cells at a normal rate accompanied by CD56dim NK cells that cannot completely acquire a terminally differentiated phenotype. Thus, our results provide evidence that support the concept that in vivo CD56bright NK cells differentiate into CD56dim NK cells, and contribute to further understand human NK cell ontogeny.
Highlights
Natural Killer (NK) cells exert cytotoxic functions and secrete IFN-c and other pro-inflammatory cytokines against virus-infected and tumor cells
We studied a case of a pediatric patient (P) that presented repeated upper airway infections and that at the age of 12 developed an ulcerative spitzoid melanoma in his right ear
The fact that within one year the patient suffered from a melanoma and a deep fungal infection in the lung led to the suspicion that the patient might be experiencing some sort of immunodeficiency
Summary
Natural Killer (NK) cells exert cytotoxic functions and secrete IFN-c and other pro-inflammatory cytokines against virus-infected and tumor cells. NK cell effector function is triggered upon recognition of target cells through activating receptors such as NKG2D, DNAM-1, 2B4, the Natural Cytotoxicity Receptors (NCRs) NKp46, NKp44 and NKp30, and members of the Killer Immunoglobulin-like Receptor (KIR) family that carry a short cytoplasmic tail (KIR2DS and KIR3DS) [4,5]. About a 90% are cytotoxic CD56dimCD16+ cells, while the remaining 10% are CD56brightCD16dim/2 non-cytotoxic cells that are abundant in secondary lymphoid organs [6,7]. This subpopulation expresses CD62L (L-selectin) and CCR7, which directs their homing to these niches but upon activation, CD62L down-regulation facilitates NK cell trafficking to inflamed tissues [8]. As mouse NK cells are different from human NK cells in many aspects [1], results from knockout mice cannot be extrapolated to humans
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