Dendritic cells

Dendritic cells also likely originate as monocytes, which then mature into dendritic cells in response to a particular signal, or series of signals. I myself am not sure precisely how dendritic cells arise, but when they have done so, they are very useful. Wikipedia perfectly describes them as "sentinels." Immature dendritic cells use PRRs - e.g. TLRs, which we've seen before - to seek out any pathogens. Some will even phagocytise small amounts of host cells in their search for anything which should not be in the body. This is rather delightfully referred to as "nibbling."

Should an immature dendritic cell successfully phagocytose a pathogen, it will mature and set about its primary function of antigen presentation - which dendritic cells do better than any other cells. Additionally, the chemokine receptor CCR7 - among other things - is upregulated, which helps guide the cell to the spleen or a lymph node. Here the dendritic cell will sensitise cells of the adaptive immune system to that particular antigen (and, therefore, the particular pathogen it has phagocytised) and a powerful response to it is occasioned.

As before, I will now give you a picture, so you can see what they look like:

(a) This is a very detailed image of a dendritic cell, taken from a journal article by Judith Behnsen et al. It is actually a screenshot of a video and the screenshot was uploaded to Wikipedia

(b) A schematic representation of a dendritic cell. (Image courtesy "A. Rad" (via Wikipedia))

Figure 1.54: The dendritic cell