conventional signal peptide, so the mechanism of 
release from the cell is unknown. 
Two IL-1 genes have also been identified in the 
mouse, and their evolution by duplication and di- 
vergence from an ancestral IL-1 gene has been es- 
tablished; however, the protein product of only the 
IL-la gene has been analyzed. 
A. Characteristics of recombinant mouse IL-1^ To 
obtain sufficient IL-1 (3 for preparation of antibodies, 
Dr. Chaplin and his colleagues expressed the pro- 
tein in Escherichia coli. When the expression vec- 
tor pMON5743 (courtesy of Dr. Peter Olins, Mon- 
santo Company) was used, recombinant 17 kDa 
IL-ip represented nearly 20% of the total bacterial 
protein. High biological potency was shown, with 
specific activity equal to that of mouse IL-la, as de- 
termined using the thymocyte coproliferation assay. 
In E. coli, 17 kDa IL-1 (3 was targeted to the bacterial 
periplasmic space. Periplasmic targeting is analogous 
to mammalian protein secretion, being dependent 
on a prokaryotic signal peptide equivalent. For 17 
kDa IL-ip, periplasmic localization was seen in the 
absence of any recognized eukaryotic or prokary- 
otic secretion signal peptide sequences. Periplasmic 
targeting was not observed with either the 31 kDa 
pro-form of IL-lp or the pro- or mature forms of 
IL-la. The molecular basis for the differential tar- 
geting behavior of recombinant 17 kDa IL-la and 
IL-ip remains unknown; however, it suggests that 
the mechanism of release of IL-lp from its normal 
cellular source may be different from that of IL-la. 
B. Preparation of anti-mouse IL-1^ antibodies. 
Rabbits and Armenian hamsters were immunized 
for the production of anti-IL-ip antibodies. All anti- 
sera and monoclonal antibodies produced by 
immunization in Freund's adjuvant recognized only 
denatured IL-1 (3 and were ineffective at neutraliz- 
ing IL-1 p biological activity, suggesting that the 
epitopes of IL-1 (3 characteristic of the biologically 
active molecule are particularly sensitive to de- 
naturation. In contrast, when animals were im- 
munized with IL-1(3 in alum, strong neutralizing 
antisera were produced in rabbits. Hamster mono- 
clonal antibodies are now being produced using 
similar protocols. 
Initial analysis of IL-1 produced by lipopolysac- 
charide-stimulated mouse peritoneal macrophages 
(PECs) using the neutralizing rabbit antiserum indi- 
cated that IL-ip represents approximately half of 
the total IL-1 produced by PECs. Pulse-chase label- 
ing experiments showed that the kinetics of biosyn- 
thesis of mouse IL-la and IL-1 (3 were similar. More 
than 90% of newly synthesized IL-la and IL-lp is 
degraded intracellularly with very little IL-1 re- 
leased from the cell. This raises the possibility that, 
in addition to its role as an immunomodulatory 
cytokine, IL-1 may have other specific intracellular 
functions. 
Dr. Chaplin is also Assistant Professor of Medi- 
cine, Genetics, and Molecular Microbiology at 
Washington University School of Medicine and As- 
sistant Physician at Barnes Hospital, St. Louis. 
PUBLICATIONS 
Articles 
Fuhlbrigge, R.C., Hogquist, K.A., Unanue, E.R., and Chaplin, D.D. 1989. Molecular biology and genetics of 
interleukin-1. Year Immunol 5:21-37. 
Fuhlbrigge, R.C., Sheehan, K.C.F., Schreiber, R.D., Chaplin, D.D. , and Unanue, E.R. 1988. Monoclonal anti- 
bodies to murine IL-la: production, characterization, and inhibition of membrane-associated IL-1 activity. 
J Immunol 141:2643-2650. 
Vik, D.R, Keeney J.B., Munoz-Canoves, P, Chaplin, D.D. , and Tack, B.F. 1988. Structure of the murine com- 
plement factor H gene. J Biol Chem 263:16720-16724. 
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