IFITM3 and influenza: Alternative splicing of human IFITMs alters their function: an N-terminus truncated IFITM2 isoform specific to immune cells displays altered antiviral specificity against HIV-1 strains [52]; while the IFITM3 rs12252-C allele is predicted to produce an aberrantly spliced N-terminus truncated IFITM3 which is associated with severe influenza, HIV-1 and COVID-19, although attempts to identify this mutant protein have thus far been unsuccessful [53–58].