The response of a host to any particular pathogen may involve the non-specific (innate) and specific (adaptive) immune system. The specific components adapt themselves to each new disease encountered and are able to generate pathogen-specific immunity. The prevalence of Escherichia coli O157:H7 has grown since its first description and despite all control measures, it remains a serious health concern. It is considered a worldwide threat not only because of its increasing incidence but also due to the severity of clinical complications during treatment, particularly its resistance to antibiotics. The need to study the infection at the cellular level, i.e. the roles played by different cells of the immune system in fighting against the infection is necessary as this will serve as a guide to the type of vaccine to be produced against the infection.