Virus in leukocytes , lymphocytes or monocytes may be protected from antibodies and other plasma components. This observation is important in HIV infection. Viruses circulating in the blood meet two important types of cells. See fig 6-4 for illustration of the above points. Role of macrophages.
Macrophages are very efficient phagocytes and present in all parts of the body.
Together with dendritic cells, macrophages are antigen processing and antigen presenting cells, and therefor play an important role in initiating the immune response. But virus can also replicate in macrophages, and there can even be enhanced replication see fig 6-5 for Kupfer cells. Differences in virus -macrophage interactions may account for differences in the virulence of virus strains and host resistance. Macrophages have Fc receptors and C3 receptors that enhance their ability to ingest viruses in the presence of complement or antibody. However in other cases if macrophages susceptible, as with dengue virus can lead to infection and antibody may enhance rather than prevent infection.