By David N. Leff

Editor's note: Science Scan is a roundup of recently published biotechnology-relevant research.

One day, your child or teen-ager wakes up with a raging, insatiable thirst and a concomitant constant urge to urinate. Soon, severe weight loss ensues, together with other symptoms, which may become fatal unless promptly diagnosed and treated.

The diagnosis, juvenile diabetes, is better defined nowadays as insulin-dependant diabetes mellitus (IDDM) Type I. Treatment of this abrupt-onset disease is a life sentence to frequent injections of the hormone insulin to replace the near-total loss of the youngster's own insulin secretion, and cope with sugar levels in the blood. Nearly 1 million diabetics in the U.S. have to shoot up insulin at least once a day in order to stay alive. (See BioWorld Today, June 10, 1999, p. 1.)

This sudden break-in and wipeout is perpetrated by a SWAT - special weapons and tactics - team, dispatched by the body's own immune system to attack and destroy the insulin-producing beta cells of the pancreatic islets of Langerhans. That onslaught is led by T lymphocytes, along with macrophages and B cells, which perceive the insulin as foe, not friend, and proceed to terminate the hormone with extreme prejudice.

This execution-style elimination of insulin is called insulitis. What triggers the autoimmune operation remains one of the main mysteries of diabetes. One favored theory is that a viral infection, perhaps mumps, starts the process. Another suggests that a switch from mother's milk to cow's milk in a nursing infant may prime the immune reaction against antigenic bovine albumin.

Determining which specific T-cell subset recognizes insulin as an alien antigen would go far toward improving therapy for Type I diabetes, perhaps by a vaccine. A long step in this direction is reported in the September 1999 issue of Nature Medicine, under the title: "Identification of an MHC [major histocompatibility] class I-restricted autoantigen in type I diabetes by screening an organ-specific cDNA library."

The immunologists at Yale School of Medicine who authored this article point out that the autoimmune process involves both CD4⁺ (helper) and CD8⁺ (cytotoxic) T cells. In one of the most faithful animal models for human diabetes, the NOD (non-obese diabetic) mouse, they identified the autoantigen recognized by highly pathogenic T cells.

Insulin is a fairly simple protein. Its 51 amino acids extend over two chains, A and B, bridged by three sulfide bonds. The Yale co-authors pinpointed the elusive peptide that stimulated the diabetogenic T cells they cloned, to eight amino acid residues, 15 through 23, on the B chain.

"This is the first identification, to our knowledge," the co-authors observed, "of an islet-reactive CD8 T-cell epitope in an autoimmune disease." They added that it "has very important implications for the potential use of insulin in preventative therapy."

Avoiding Needle, DNA Vaccine Splashed On Mouse Skin Sneaks In Via Hair Follicles

One limitation of current vaccination is the "ouch factor." Many people, especially children, flinch from needle injection. Dermatologists and molecular pharmacologists at Stanford University report a way around this and other existing drawbacks in immunization. The title of their paper in the September issue of Nature Biotechnology tells how: "Immunization via hair follicles by topical application of naked DNA to normal skin."

The co-authors pipetted droplets of naked plasmid DNA dissolved in saline onto the unprepared skin of normal mice. Their plasmid payload consisted of the commercially available recombinant hepatitis B surface antigen (HBsAg) polypeptide vaccine, which is injected intramuscularly. Comparing that route with their skin-dribbled topical vaccine, the co-authors found, "Topical DNA vector administration induced immunoglobulin G class antibodies against HBsAg at a titer 34.4 percent that of intramuscular polypeptide vaccination." They added, "In addition to inducing a humoral [antibody] immune response, topical vaccination produced specific cell proliferative responses to HBsAg polypetide at a magnitude of 46 percent that of intramuscular administration, [and this] could be sustained for over six months."

Penetration of their through-the-skin vaccine, they explained, uses hair follicles as conduits.

Tokyo Neuroscientists Connect Dots Confirming Gad Gene's Role In Protein Garbage Disposal

Getting rid of surplus proteins in a cell requires garbage disposal machinery as elaborate as that for protein synthesis. This intracellular protein breakdown is managed by a specialized molecule called ubiquitin. Ubiquitination tags proteins in the cell that are targeted for degradation. The ubiquitin-proteosome complex then does that dirty work. When the ubiquitin carboxy-terminal hydrolase gene is mutated, it causes a neurodegenerative disease in mice called gracile [thin] axonal dystrophy. Gad mice are reputed to make good models of human neurodegenerative diseases. Among other features, they develop motor ataxia.

The brains of these rodents contain spherical dots of ubiquitin-conjugated protein in moribund nerve terminals and axons. The tiny spheroids seem to hold clues to the pathogenic processes in such human diseases as Alzheimer's, Parkinson's and Huntington's, but efforts to connect these dots to defects in the cellular degradation mechanism have failed so far.

But perhaps no further. A group of Japanese neuroscientists at the National Institute of Neuroscience in Tokyo have wrestled with this puzzle for over a decade. Now they report new findings in the September 1999 issue of Nature Genetics. Their paper is titled: "Intragenic deletion in the gene encoding ubiquitin carboxy-terminal hydrolase in gad mice."

It traces the murine gad mutation to a deletion in the gene, which is selectively expressed in the nervous system and testis. The mutated DNA lacks a 42-amino-acid segment that contains a catalytic residue. Hence, is appears to compromise protein turnover by ubiquitin. "Our data," the co-authors write, "suggest that altered function of the ubiquitin system directly causes neurodegeneration. The gad mouse," they conclude, "provides a useful model for investigating human neurodegenerative disorders."