Alternative splicing of cell surface receptors in Homo sapiens that play a role in HIV and parasite infections. (A) Sequence data was available to construct a diagram showing splicing for 4 CD45 isoforms. These isoforms arise due to the alternate splicing of introns 4–6. The resulting mRNAs differ drastically in size and sequence. The CD45 gene is 125 kbp in size with a large intron between exons 2 and 3. Isoforms 1 and 2 contain multiple exons dispersed across a large 60 kbp stretch of DNA. (B) Two CCR5 arise due to alternative splicing of a transcript derived from an alternative upstream promoter. The larger isoform negatively controls the expression of the smaller isoform. (C) Two CXCR3 isoforms have been identified which interact with the same chemokines but, this interaction results in opposing signaling based on the isoform present.