Different groups of C-type lectins (CTLs) and their domain structures. (A) Sixteen groups are shown, defined by their phylogenetic relationships and domain structures. Some of the groups are soluble proteins and others are transmembrane proteins. (B) The group 3 collectins form oligomeric structures, shown as cruciform and bouquet structures in the box. Each of the domains is named as indicated in the key. For abbreviations see the text.