I. Genes and Structures of IL-5 The cDNA encoding murine IL-5/TRF/BCGFII was cloned by using SP6 expression vector system(22, 27). The amino acid sequence deduced from the nucleotide sequence of the entire IL-5 cDNA revealed that murine IL-5 consists of 133 amino acids including a hydrophobic signal sequence of 20 amino acids (27) with a molecular mass of 12.3 kDa. Three potential N-glycosylation sites as well as three cystein residues are present in the polypeptide sequence. The deduced amino acid sequence of murine IL-5 failed to show any significant homology to all the cytokines so far identified, except for short sequences of murine IL-3, murine granulocyte-macrophage colony-stimulating factor(GM-CSF) and murine IFN-ƒÁ (27). Using the mouse IL-5 cDNA as a probe, we isolated the human IL-5 cDNA (2). Human IL-5 consists of 134 amino acids with a typical signal sequence of 19 residues. Comparison of the cDNA sequence of murine IL-5 with that of human shows a sequence homology of 77% at the DNA level and 70% at the protein level. The chromosomal genes for murine and human IL-5 were isolated using the respective IL-5 cDNA as probes(9, 41, 68). Nucleotide sequence analyses of the IL-5 gene as well as flanking regions show that the IL-5 gene consists of 4 exons 3 introns. Conserved TATA-like and lymphokine consensus sequences are found at about 30 and 70 base pairs (bp), respectively, upstream of the transcription initiation sites. As the exon-intron organization and the location of the cystein codons of the IL-5 genes resemble those of the GM-CSF, IL-2, IL-4 genes but are quite distinct from those of G-CSF(41). The human IL-5 gene was mapped to chromosome 5823.1-31.1 on which IL-4, GM-CSF, and IL-3 genes are mapped(8, 59). Murine IL-5 gene is located on chromosome 11. It is likely that the IL-4 and IL-5 genes are clustered with the GM-CSF and IL-3 genes on human chromosome 5 and murine chromosome 11 (3) and that these genes might be derived from a com monancestral gene by duplications.

In mouse, IL-5-producing T-cell hybrid(B151) constitutively expressed the IL-5 message of which expression could be augmented by the stimulation with phorbol myristate acetate(PMA) plus calcium ionophore(69). Cloned murine T cell lines of TH2-type as well as TH2-type-transformed T cell lines can also express IL-5 mRNA, accompanying with IL-5 production, upon stimulation with PMA or Con A. T cells from Mycobacterium-primed mice and nematode-infected mice could express the IL-5 mRNA upon stimulation with purified protein derivatives (PPD) and nematode-antigen, respectively(69, 79). In contrast, normal spleen