KLRD1 and infection: While PIV5 is largely noncytopathic toward the tumor cell itself [43,44,45], we have shown previously that PIV5 infection contributes additional signals for PM21-NK cell killing of lung cancer cells through cell surface expression of the viral hemagglutinin-neuraminidase (HN) glycoprotein [26], which is recognized by NK cell receptor NKp46 [46].