Synopsis of the structure of VLPs.

a As illustrated by the expression of influenza virus hemagglutinin alone or the co-expression of hemagglutinin and neuraminidase, expressed in enveloped VLPs, a single layer can be formed by the expression of 1 (i) or 2 glycoproteins. A single-layer VLP will also result from the expression of over three glycoproteins (iii). 2 (iv) or more than 3 glycoproteins (v) may be present on the surface of double-layered enveloped VLPs, which are capable of forming such structures. b A single protein (i) or 2 proteins (ii) may be utilized in the assembly of single layered non-enveloped VLPs. 2 proteins (iii) or greater than 3 proteins (iv) may be utilized in the construction of double-layered non-enveloped VLPs. In excess of 3 proteins, triple-layered VLPs (v) have been constructed.