Lysozymum

A shuttle vector plasmid, pYZ289, was constructed from the pZ189 plasmid and polyoma virus DNA. The plasmid contains a supF gene as a marker of mutation and can replicate in both Escherichia coli and mouse cells. The pYZ289 plasmids treated with N-methyl-N-nitrosourea were passed through mouse cells originating from skin tumors, which are either proficient (HL18) or deficient (HL8) in O6-methylguanine-DNA methyltransferase activity, and mutations in the supF gene were analyzed. In the repair-deficient HL8 cells, N-methyl-N-nitrosourea-treated pYZ289 showed lower plasmid survival and higher mutation frequency than in the repair-proficient HL18 cells. DNA sequence analysis in the mutated supF gene revealed that most mutations occurred in G:C base pairs (86% for HL8, 76% for HL18), and the frequency of G:C----A:T transition was higher in HL8 cells (69%) than in HL18 cells (31%). G:C----T:A transversions occurred more frequently in HL18 cells (31%) than in HL8 cells (12%). Mutations occurred frequently at the base pair positions of 123 and 159 of supF gene in HL18 cells and at 169 in HL8 cells. Analysis of the bases neighboring the mutations appeared to be related to the mutability of the base pairs with the sequence of 5'-purine-G-G-3' being the most frequently mutated.

OBJECTIVES: ;Intravital microscopy is a useful tool for studying leukocyte trafficking in atherosclerosis. However, distinction between various subclasses of leukocytes using this technology is lacking. Therefore, we generated ApoE(-/-)/Lysozyme M(EGFP/EGFP) mice and investigated whether targeted cell types could be visualized by in vivo microscopy and whether absence of lysozyme M will influence atherosclerosis.;METHODS: ;We crossed male ApoE(-/-) mice with mice homozygous for a knock-in mutation of enhanced green fluorescent protein (EGFP) in the lysozyme M locus (Lys(EGFP/EGFP)) creating ApoE(-/-)/Lys(EGFP/EGFP) mice. Mice were sacrificed at the age of 26 weeks. Blood was collected for serum lipid analysis, differential white blood cell count and flow cytometry. Lesion area was determined on en face mounted aortas and sections from aortic roots were stained for immunohistochemistry. Atherosclerotic lesions were also studied by confocal- and intravital microscopy.;RESULTS: ;Basic parameters, such as white blood cell count, cholesterol profile, lesion area and plaque composition was unaltered in ApoE(-/-)/Lys(EGFP/EGFP) mice compared to ApoE(-/-) mice. Fluorescent neutrophils and monocytes were clearly visualized by intravital fluorescence and confocal microscopy.

Efficient induction of self tolerance is critical for avoiding autoimmunity. The T cells specific for the well-processed and -presented (dominant) determinants of a native self protein are generally tolerized in the thymus, whereas those potentially directed against the inefficiently processed and presented (cryptic) self epitopes escape tolerance induction. We examined whether the crypticity of certain determinants of mouse lysozyme-M (ML-M) could be attributed to the nonavailability of a proteolytic site, and whether it could be reversed to immunodominance by engraftment of a novel cleavage site in the flanking region of the epitope. Using site-directed mutagenesis, we created the dibasic motif (RR or RK; R = arginine, K = lysine), a target of intracellular proteases, in the region adjoining one of the three cryptic epitopes (46-61, 66-79, or 105-119) of ML-M. Interestingly, the mutated lysozyme proteins, but not unmutated ML-M, were immunogenic in mice. The T cell response to the altered lysozyme was attributable to the efficient processing and presentation of the previously cryptic epitope, and this response was both epitope and MHC haplotype specific. In addition, the anti-self T cell response was associated with the generation of autoantibodies against self lysozyme.