Cytomegaloviruses (CMVs) are ubiquitous in nature, having evolved over many millenia with their hosts. While in healthy hosts most infections with CMV are asymptomatic, the virus can cause severe disease in immunocompromised hosts. Thus, the increase in organ transplantation and the HIV/AIDS pandemic have established human CMV (HCMV) as a clinically important pathogen. Indeed, HCMV infections are now the major cause of morbidity and mortality among immunocompromised patients, which has led to more research targeting CMV for effective anti-viral treatment. The discovery that cytomegaloviruses encode several genes which are involved in immune escape has prompted a new area of research, aimed at understanding immune escape mechanisms for exploitation as potential anti-viral therapeutics. By targeting the viral proteins directly, or their receptors in the host, it may be possible to treat CMV disease by agonistic/antagonistic therapy. The first part of this thesis describes the first demonstration of anti-NK1.1 staining in situ to identify NK cells using a modified in vivo perfusion/fixation method. Using this method, we have compared the acute NK1.1+ cellular response to wild-type MCMV infection in the visceral organs of genetically susceptible intra-NK complex recombinant BALB.B6-CT6 (Cmv1s, NK1.1+) mice with resistant C57B⁄J (Cmv1r, NK1.1+) and BALB.B6-Cmv1r mice (Cmv1r, NK1.1+). Expression of viral antigens and the consequences of infection on other cellular subsets, were also analyzed in this study. The data show that in susceptible mice (Cmv1s) MCMV infection is predominent in the marginal zone of splenic white pulp, resulting in local changes in various cellular constituents, including macrophages, NK cells and DC. In the liver, distinct foci of infection were comprised of large numbers of macrophages and NK1.1+ cells surrounding infected cytomegalic cells. In resistant mice (Cmv1r), 6 MCMV infection predominantly affected the red-pulp of the spleen and was associated with increased accumulation of NK1.1+ cells and macrophages at sites of viral infection