Up to 60% of cases of the autosomal recessive immunodeficiency
hemophagocytic lymphohistiocytosis (HLH) are associated with mutations in the
perforin (PRF1) gene. In this study, we expressed wild-type and mutated
perforin in rat basophil
leukemia cells to study the effect on lytic function of the substitutions A91V and N252S (commonly considered to be neutral polymorphisms) and 22
perforin missense substitutions first identified in HLH patients. Surprisingly, we found that A91V
perforin was expressed at reduced levels compared with wild-type
perforin, resulting in partial loss of lytic capacity. In contrast, expression and function of N252S-substituted
perforin were normal. Most HLH-associated mutations resulted in protein degradation (probably due to misfolding) and complete loss of
perforin activity, the exception being R232H, which retained approximately 30% wild-type activity. Several other mutated
proteins (H222Q, C73R, F157V, and D313V) had no detectable lytic activity but were expressed at normal levels, suggesting that their functional defect might map downstream at the level of the target cell membrane. One further
perforin substitution identified in an HLH patient (V183G) was normally expressed and displayed normal lysis. This report represents the first systematic functional analysis of HLH-associated missense mutations and the 2 most common
perforin polymorphisms.