Rat dorsal root ganglia neurons as a model for Listeria monocytogenes infections in culture

Neurotropism of Listeria monocytogenes was studied in rat dorsal root ganglia (DRG) and hippocampal neurons in culture. Using a system in which the DRG neurons can grow relatively free from other cells, it was observed that such DRG neurons, in contrast to hippocampal neurons, can be effectively infected by L. monocytogenes. The bacteria aligned along DRG axons, but not along hippocampal neurites. A mutant deficient in internalin, a protein required for entry into E-cadherin-expressing cells, did not interact with DRG neurons. Axonal migration of bacteria was studied in the DRG neurons grown in a double-chamber system, where either the neurites or the nerve cell bodies were exposed to the bacteria. The data suggest that L. monocytogenes can infect both axons and DRG nerve cell bodies, and that the bacteria can migrate in a retrograde as well as anterograde direction. These results support the notion that L. monocytogenes can spread via primary sensory neurons to the central nervous system. Infection of DRG primary sensory neurons, as employed in the present study, provides a model for analysis of bacterial and neuronal factors of importance for neurovirulence of L. monocytogenes. Received: 3 April 1999     

Immunochemical aspects of Fc-mediated binding of human IgG subclasses to group A, C and G streptococci

Nineteen human IgG myeloma proteins were tested in a sensitive assay for binding to 60 strains of β-hemolytic streptococci. Human group A, C and G streptococci demonstrated strong reactivity with positive binding of all four human IgG subclasses. Group C and G streptococci were capable of binding twice as much IgG as group A strains. β-Hemolytic bovine group G streptococci showed a low degree of reactivity with IgG1 and IgG4. Kinetic experiments revealed that the IgG binding was a time-dependent, displaceable process. Studies performed with Fab and Fc fragments showed that Fc structures are involved in the binding of intact IgG molecules to the bacterial cell surface. In addition, radiolabelied Fab fragments from two monoclonal components exhibited a definite reactivity with group G streptococci. Scatchard plots of the IgG-streptococcal interaction showed a linear section at low saturation levels. The equilibrium constants derived from such plots were 8–9 × 10⁷ 1./mole. The equilibrium constant for the interaction of IgG with staphylococcal protein A as measured with the Cowan I reference strain was 5 × 10⁷ 1./mole.