Abstract 151

Background: A number of surface markers has been identified which modulate cytotoxicity of natural killer cells (NK cells): killer cell inhibitory receptors (KIR), and killer cell activatory receptors (KAR). The complex interaction of KIR-/KAR-expression is not fully understood. We investigated KIR-expression of highly enriched CD56+ cells derived from healthy newborn infants (neonates) and adult peripheral blood(controls).

Material and Measurements: CD56+ cells were purified by immunomagnetic isolation (MACS), cord blood (n=12), adult controls (n=5). Cells were stained with KIR-/KAR-specific monoclonal antibodies HP-3B1(CD94), EB6 (CD158a), GL183 (CD158b), DX9 (NKB1) and 5.133 (NKB1+NKAT4). Flow cytometric analysis (FACScan) was restricted to CD56+ cells.

Results: CD56+ cells, isolated with a purity of 97.2± 1.4% (±SD) in neonates and 93.9 ± 1.8% in adult controls, displayed a heterogenous pattern of KIR-expression. 9.4 ± 5.0% [14.2 ± 6.9%] cord blood CD56+ cells [adult controls] stained positive for DX9, 12.7 ± 3.6% [18.0 ± 7.4%] for 5.133, 20.0 ± 8.1% [23.9 ± 5.0%] for EB6, 20.5 ± 5.7% [25.0± 6.0%] for GL183 and 90.1 ± 5.8% [72.8 ± 10.6%] for HP-3B1. Compared to adult CD56+ cells, expression of CD94 (HP-3B1) was significantly increased in cord blood CD56+ cells (90 vs. 73%, p<0.01) whereas expression detected by DX9, 5.133, GL183 and EB6 was lower in cord blood samples.

Conclusions: Neonatal and adult CD56+ cells displayed a similar pattern of killer cell inhibitory receptors. The extent of receptor expression, however, differed between cord blood and adult CD56+ cells. The deficits in NK cells of newborns in antigen dependent cell mediated cytotoxicity may be explained - at least in part - by differences in KIR-/KAR-expression.

Supported by fortüne 328, University of Tübingen