Worm Breeder's Gazette 14(2): 32 (February 1, 1996)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Department of Insect Physiology and Behavior, National Institute of Sericultural and Entomological Science, Tsukuba, Ibaraki 305, Japan
The B- and T-cell based adaptive immunity is thought to be found only in vertebrates. In contrast, several systems categorized in innate immunity (e.g. the defense by phagocytes, superoxides, and antibacterial proteins etc) have been reported in many species of animals, both vertebrates and invertebrates. It might be worthwhile if we can study the innate immunity of nematodes, because of the utility of C. elegans. Previously, we reported that at least three humoral defense activities (antibacterial, bacteriolytic, and agglutinating) were detected in the body fluid of the parasitic nematode Ascaris suum (1). The substantial nature of these activities was suggested to be proteins/peptides, because all of them were lost by trypsin digestion. One of them, ASABF (Ascaris suum antibacterial factor) is a heat-stable antibacterial protein with molecular mass of 7 kDa. Recently, we purified ASABF, and its amino acid sequence was determined. Eight Cys residues which might contribute to intramolecular disulfide bonds were found in this sequence. MPsrch data base searches revealed weak sequence identity between ASABF and insect/arthropod defensins (IADs), the antibacterial proteins which contain 6 Cys residues (2). Jumbling test supported that this similarity was significant. All of them were positively charged proteins. In addition, Gram-positive bacteria were much more sensitive to ASABF (IC50=0.6 microgram/ml, against Staphylococcus aureus) than Gram-negative bacteria (IC50=50 microgram/ml, against Esherichia coli), and this antibacterial spectrum is similar to IADs. However, ASABF consisted of over 60 residues, whereas IADs consisted of only 30-40 residues. The positions of Cys residues in the sequence of IADs were highly conserved, and they are essential to the antibacterial activity. In contrast, an additional Cys of ASABF was found at the internal position of conserved array of Cys residues. ASABF, therefore, is not a typical IAD, although ASABF might be evolutionally related to IADs. Many antibacterial proteins have been isolated from various insect sources. Their gene regulation mechanisms have been explored in Drosophila and other insects. Interestingly, similar regulatory factors which originally found in vertebrates (e.g. NFkappaB) was also essential in insects. Its relationship to factors involved in embryonic pattern formation has been discussed (Dif and dorsal)(3, 4). What will be found in the ASABF genes? The sequencing of cDNAs and genes of ASABF, and the search for its homologues in C.elegans are currently proceeding. (1) Kato, Y. (1995) Zool. Sci. 12, 225-230. (2) Boman, H.G. (1995) Annu. Rev. Immunol. 13, 61-92. (3) Ip, Y.T. et al. (1993) Cell 75, 753-763. (4) Hoffmann, J.A. (1995) J. Cell. Biochem. 21A, 188 (an abstract for Keystone symposia 1995)