Statistical analysis of the distribution of gold particles over antigen sites after immunogold labelling

The locations of immunogold-labelled particles on ultrathin sections of pellets of purified tobacco rattle virus were analysed statistically. The distributions were found to be inconsistent with a Poisson process. Instead, a physically based model, a modified Poisson process, is proposed and shown to fit the data well. The antigen sites to which antibodies are attached are assumed to follow a Poisson process and one gold particle sits on top of each site. However, if two sites are closer than a threshold then the physical size of the gold particles with attached antibodies pushes the particles apart, and if sites are nearer than a higher threshold there is a chance that surface tension will pull the gold particles together.