Michael J. Lloyd and Dr. Gregory F. Burton, Microbiology
Measles virus continues to be a major cause of death in most third-world countries and a considerable threat to the health of every country. Infection with measles is thought to be associated with the fatal, late-infection disease subacute sclerosing panencephalitis (SSPE) (3). It is thought that Measles virus is retained by the body following infection until it mutates, crosses the blood-brain barrier to infect and destroy brain tissue, killing the host.
Follicular Dendritic Cells (FDC) are crucial elements of the body’s immune system, they help the body remember encountered antigens by retaining some of that antigen on their surface. FDC form networks in secondary lymphoid tissue, such as lymph nodes and the spleen, to retain conventional antigens. My hypothesis is that FDC bind Measles Virus in an infectious form for long periods of time. Support for the concept of FDC protecting virus particles and maintaining their infectious nature comes from studies using the Human Immunodeficiency Virus (HIV-1). As seen in Figure 1, FDC hold antigen complexes on their long dendritic processes so the body will “remember” the antigen (2,4). Studies show that FDC trap, retain HIV, and preserve its infectivity for many months (1). My research has shown that FDC also have the ability to hold Measles Virus on their surface in an infectious form.
FDC were extracted either from human tonsilar samples or from murine lymph nodes. After isolation by centrifugation and magnetic bead exclusion, FDC were used for TCID50 assays that show whether the virus in question is infectious by the damage it does to the cell (cytopathic effects – CPE.) African Green Monkey Kidney Cells (C1008 or Vero) were cultured in 48-well plate overnight to give 50% confluency. Destruction of the C1008 cells by the Measles Virus received a “+” marking for positive CPE. Dr. F. Brent Johnson (Department of Microbiology, BYU) provided Measles Virus as a kind gift for our use. Dr. Christopher Karp (Department of Pathology, Johns Hopkins University) provided human antibody to Measles Virus. According to Table 1 (below), Measles Virus was incubated with human antibody for two hours at 4°C and then either put in the well with the Vero cells or incubated for two additional hours with FDC at 4°C. The results are shown in Table 1.
The second column (“Vero + Measles + Antibody”) shows the Measles virus is infectious and will destroy the C1008 cells. The third column (“Vero + FDC”) shows that the FDC have no cytopathic nature in and of themselves. Column four (“Vero + FDC + Measles + Antibody”) shows that the FDC will hold bound Measles complexes in an infectious form and transfer infection to the C1008 cells. Finally, the fifth column (“Vero + FDC wash”) proves there is nothing in the FDC culture that could produce the CPE shown in column four.
These results indicate that FDC have the ability to hold infectious Measles Virus and antibody complexes on their surface. This in-vitro experiment may reflect in-vivo processes within the human body. In addition, these preliminary data encourage further study as to the processes involved in loading the virus/antibody complexes onto the surface of the FDCs. I propose further studies to show the role of complement in FDC antigen loading. I believe that complement proteins can augment the ability of FDCs to bind and retain complexed antigen.
References
- Burton, G., Masuda, A., Heath, S., Smith, B., Tew, J., Szakal, A. Folliculare dendritic cells (FDC) in retroviral infection; host/pathogen perspectives. Immunological Reviews. 1997, Vol 156: p185-197.
- Janeway, Charles A., et al. Immunobiology the Immune System in Health and Disease Garland Publishing, 1997.
- White, David O., et al. Medical Virology, Fourth Edition Academic Press 1994.
- Szakal, A.K., Gieringer, R.L., Kosco, M.H., Tew, J.G.: Isolated follicular dendritic cells: cytochemical antigen localization, Nomarski, SEM and TEM morphology. The Journal of Immunology. 134: 1349-1359.