Alternative splicing is defined as a process that increases the diversity of transcripts and protein variety. It is estimated that 5–30% of human genes express alternative variants. Alternative splicing is regulated by different, tissue-specific splicing enhancers and silencers. Numerous proteins are the products of this process, as for example 15-lipoxygenase-b and cyclooxygenase. Alternative variants of proteins may have different functions like for example IL-4.