Plasmacytoid dendritic cells: Friend or Foe?

Plasmacytoid dendritic cells (look a lot like plasma B cells but express different proteins on their cell surface) are important interferon-producers in the presence of viral RNA or DNA (an interferon is a cytokine, or a signaling protein released in response to a pathogens).  pDCs are important in linking the innate (nonspecific) and adaptive (specific) immune response through increasing the function of natural killer and T cells, respectfully.

Much is still unknown about pDC function, though.  As discussed in Li et al., there is a debate on whether pDCs inhibit HIV/SIV replication or instead promote chronic immune activations and disease.  In other words, what is the role of pDCs in lentiviral (long incubation period) infections?  Using SIV (Simian immunodeficiency viruses)-infected rhesus monkeys, Li et al. tried to determine the systematic distribution of pDCs using a cell counting/sorting mechanism called flow cytometry.  They also looked their cytokine expression and affect on T cell activation upon infection. 

 In their study, Li et al. found that chronic SIV infection redistributed pDCs from the blood and lymphoid organs to the gut and gut associated draining lymph nodes, described as “gut-homing.”  Also, infection caused pDCs to secrete an increase in specific proteins (ex. TNF-alpha and INF-alpha cytokines) used to communicate/activate with other immune cells.  These two results are consistent with prolonged immune activity that is linked to progressive diseases, like cancer, cardiovascular problems, and liver and kidney failure, as seen in HIV infections. 

So why should you care about this?  Well, by better understanding how our immune system responds to pathogens, both in positive and negative ways, we are more capable to treat and even prevent complex diseases like HIV, where many develop problems that arise from the elevated level of the immune response rather than the virus itself. 

Primary article:

Li, H., Gillis, R., Johnson, R. & Reeves, R. (2013). Multi-functional plasmacytoid dendritic cells redistribute to gut tissues during simian immunodeficiency virus infection. Immunology, 140(2), 224-9. doi:http://onlinelibrary.wiley.com/doi/10.1111/imm.12132/abstract;jsessionid=1689DA62A55C5ADC438859F2190D8475.f02t02

pDC background:

Colonna, M., Trinchieri, G. & Liu, Y. (2004). Plasmacytoid dendritic cells in immunity. Nat Immunol, 5(12), 1219-26. doi: http://dx.doi.org/10.1038/ni1141

pDC image:

http://www.s-ibm.org/data/pathology_data/#1

Adorable rhesus monkey image:

http://animals.nationalgeographic.com/animals/mammals/rhesus-monkey/