The ability of antibody (Ab) to modulate HSV pathogenesis is well recognized but the mechanisms by which HSV-specific IgG antibodies protect against genital HSV-2 disease are not well understood. The requirement for Ab interactions with Fcgamma receptors (FcgammaR) in protection was examined using a murine model of genital HSV-2 infection. IgG antibodies isolated from the serum of HSV-immune mice protected normal mice against HSV-2 disease when administered prior to genital HSV-2 inoculation. However, protection was significantly diminished in recipient mice lacking the gamma chain subunit utilized in FcgammaRI, FcgammaRIII, FcgammaRIV and FcepsilonRI receptors and in normal mice depleted of Gr-1(+) immune cell populations known to express FcgammaR, suggesting protection was largely mediated by an FcgammaR-dependent mechanism. To test whether neutralizing Ab might provide superior protection, a highly neutralizing HSV glycoprotein D (gD)-specific monoclonal antibody (mAb) was utilized. Similar to results with HSV-specific polyclonal IgG, administration of the gD-specific mAb did not prevent initial infection of the genital tract but resulted in lower virus loads in the vaginal epithelium and provided significant protection against disease and acute infection of the sensory ganglia; however, this protection was independent of host FcgammaR expression and was manifest in mice depleted of Gr-1(+) immune cells. Together, these data demonstrate that substantial Ab-mediated protection against genital HSV-2 disease could be achieved by either FcgammaR-dependent or -independent mechanisms. These studies suggest that HSV vaccines might need to elicit multiple, diverse antibody effector mechanisms to achieve optimal protection.

Zinc salt solutions administered as topical microbicides provided significant protection against herpes simplex virus type 2 infection in a mouse vaginal challenge model. However, at the therapeutic concentration, the salt solutions caused sloughing of sheets of vaginal epithelial cells. These observations limit the utility of zinc salts as microbicides and suggest that the application of zinc solutions to mucosal surfaces has the potential to cause damage that might increase susceptibility to secondary infections at a later time.

The tissue sites of long-term herpes simplex virus type 2 (HSV-2)-specific antibody production in mice and guinea pigs were identified. In addition to secondary lymphoid tissue and bone marrow, HSV-specific plasma cells were detected in spinal cords of mice up to 10 months after intravaginal inoculation with a thymidine kinase-deficient HSV-2 strain and in lumbosacral ganglia and spinal cords of guinea pigs inoculated with HSV-2 strain MS. The long-term retention of virus-specific plasma cells in the peripheral and central nervous systems following HSV infection may be important for resistance to reinfection of neuronal tissues or may play a role in modulation of reactivation from latency.

Previously, the histidine residue at position 16 in the mature T4 pyrimidine dimer glycosylase (T4-PDG) protein has been suggested to be involved in general (nontarget) DNA binding. This interpretation is likely correct, but, in and of itself, cannot account for the most dramatic phenotype of mutants at this position: their inability to restore ultraviolet light resistance to a DNA repair-deficient Escherichia coli strain. Accordingly, this residue has been mutated to serine, glutamic, aspartic acid, lysine, cysteine, and alanine. The mutant proteins were expressed, purified, and their abilities to carry out several functions of T4-PDG were assessed. The mutant proteins were able to perform most functions tested in vitro, albeit at reduced rates compared with the wild type protein. The most likely explanation for the biochemical phenotypes of the mutants is that the histidine residue is required for rapid turnover of the enzyme. This role is interpreted and discussed in the context of a reaction mechanism able to account for the complete spectrum of products generated by T4-PDG during a single turnover cycle. The base excision repair (BER)1 glycosylases initiate DNA repair by recognizing inappropriate or damaged DNA bases and removing them via glycosyl bond scission (1). These enzymes are responsible for the substrate specificity of their particular BER pathways, a formidable accomplishment, as this recognition must proceed within the context of a vast excess of perfectly normal and appropriate bases. A subset of these enzymes also carry out scission of the DNA sugar-phosphate backbone by ␤-elimination and adjacent to the site of glycosyl bond cleavage. These enzymes will be referred to as "BER glycosylase-lyases." Enzymes in this subset of glycosylases utilize a primary or secondary amino group as an active site nucleophile. The amino group adds to C 1 Ј because of the developing electrophilic character of that carbon accompanying glycosyl bond cleavage. The resulting Schiff base enzyme-DNA intermediate, in its protonated form, has been proposed to kinetically assist DNA backbone cleavage (2). Gerlt (3) has hypothesized that the rate of the ␤-elimination reaction is directly determined by the acidity of the 2Ј-hydrogens on the sugar undergoing 3Ј-phosphate group elimination. Within this hypothesis, the role of the protonated Schiff base would be to lower the pK a of the 2Ј-hydrogens. In the proposed reaction scheme, one of these hydrogens would be abstracted by a general base, either an activated water or a basic amino acid side chain. T4-PDG is a ultraviolet light (UV) pyrimidine photodimer-specific BER glycosylase-lyase similar mechanistically to other BER glycosylase-lyases. The N-terminal threonine ␣-amino group is the active site nucleophile (4).To investigate those amino acid candidates whose side chains might serve as general bases for abstracting a sugar 2Ј-hydrogen to initiate the ␤-elimination reaction, we identified all amino acid side chains within 10 Å of the ␣-amino nitrogen in the cocrystal struc...

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