Kode FSL constructs consist of three components; a functional moiety (F), a spacer (S) and a lipid (L).
Function groups on FSL constructs that can be used to create kodecytes include saccharides (including ABO blood group-related determinants, sialic acids, hyaluronin polysaccharides), fluorophores, biotin, and a range of peptides.
Although kodecytes are created by modifying natural cells, they are different from natural cells. For example, FSL constructs, influenced by the composition of the lipid tail, are laterally mobile in the membrane and some FSL constructs may also cluster due to the characteristics of the functional group (F). As FSL constructs are anchored in the membrane via a lipid tail (L) it is believed they do not participate in signal transduction, but may be designed to act as agonists or antagonists of the initial binding event. FSL constructs will not actively pass through the plasma membrane but may enter the cell via membrane invagination and endocytosis.
The "koding" of cells is stable (subject to the rate of turnover of the membrane components). FSL constructs will remain in the membrane of inactive cells (e.g. red blood cells) for the life of the cell provided it is stored in lipid free media. In the peripheral circulation FSL constructs are observed to be lost from red cell kodecytes at a rate of about 1% per hour. The initial "koding" dose and the minimum level required for detection determine how long the presence of "kodecytes" in the circulation can be monitored. For red blood "kodecytes" reliable monitoring of the presence of the "kodecytes" for up to 3 days post intravenous administration has been demonstrated in small mammals.
The spacer (S) of a FSL construct has been selected so as to have negligible cross-reactivity with serum antibodies so kodecytes can be used with undiluted serum. By increasing the length of the FSL spacer from 1.9 to 7.2 nm it has been shown sensitivity can improve two-fold in red cell agglutination based kodecyte assays. However, increasing the size of the spacer further from 7.2 to 11.5 nm did not result in any further enhancement.