Native SP-A is thought to consist of hetero-oligomers of SP-A1 and SP-A2, and properties of co-expressed SP-A1/SP-A2 are between those of SP-A1 and SP-A2 [41, 46] . However, the extent of oligomerization of SP-A, as well as the SP-A1/SP-A2 ratio, may be altered in various diseases and can vary among individuals [53, 54] . The combination of both gene products may be important for reaching a fully native conformation [41] . In fact, it was recently shown that both SP-A1 and SP-A2 are necessary for the formation of pulmonar tubular myelin [55] . Therefore, the effect of a given haplotype may be largely influenced by haplotypes at the other gene. Our results suggest that the 6A 2 to1A 0 haplotype is more protective against CAP than both 6A 2 and 1A 0 .