Use of monoclonal antibodies that recognize p60 for identification of Listeria monocytogenes.

Listeria monocytogenes causes major food-borne outbreaks of disease worldwide. Specific identification of this microorganism is of utmost importance to public health and industry. Listeria species are known to secrete a 60-kDa protein collectively termed p60, which is encoded by the iap (invasion-associated protein) gene and secreted in large quantities into the growth media. p60 is a highly immunogenic murein hydrolase that is essential for cell division. Due to these properties, p60 is an ideal diagnostic target for the development of immunological detection systems for L. monocytogenes. We report here two independent lines of monoclonal antibody (MAb): p6007, which specifically recognizes L. monocytogenes p60, and p6017, which reacts with a wide range of Listeria p60 proteins. By combining these antibodies with a polyclonal antibody, we developed efficient sandwich enzyme-linked immunosorbent assay (ELISA) systems which can specifically identify L. monocytogenes or generally detect Listeria species. Since an excess amount of the peptide corresponding to PepA or PepD did not interfere with the ELISA, and direct ELISAs were unable to detect both peptides, we concluded that the epitope presumed to be recognized by p6007 or p6017 could be distinguished from PepA and PepD as described by Bubert et al. (Appl. Environ. Microbiol. 60:3120-3127, 1997). To our best knowledge, this is the first example of an immunological identification system that uses p60-recognizing MAbs.

Immunity in the absence of CD28 and CD137 (4-1BB) molecules.

We report the generation and immune regulation of mice that are deficient in CD28 and 4-1BB (CD137) genes. These mice were viable, fertile and did not display any overt abnormalities and had a normal T cell phenotype in thymus and spleen. Proliferative responses to anti-CD3 and ConA were enhanced in 4-1BB-/- but not in either CD28-/- or double mutant mice, while levels of interleukin-2 were decreased in all mutant mice. Although the 4-1BB-/- mice displayed increased basal levels of most immunoglobulin isotypes tested, the plateau levels of immunoglobulin G2a, immunoglobulin G2b and immunoglobulin A were particularly high compared to wild type controls. The immunoglobulin class switch to T-dependent antigen was normal in 4-1BB-/- mice but was greatly affected in both CD28-/- and 4-1BB-/- CD28-/- mice. Vesicular stomatitis virus-specific cytotoxic T lymphocyte responses and plaque reduction neutralizing ability was differentially reduced in all mutant mice. Contact sensitivity to allergens showed marginal but not significant change in ear thickness in 4-1BB-/- mice, but an ability to mount contact hypersensitivity to the same antigens was greatly curtailed in CD28-/- and double mutant mice.