Question

Explain that the action of the dendritic cell is part of both the nonspecific second line of defense and the specific immune response in the third line of defense. (use the terms TLR- toll like receptor, PAMP-pathogen associated molecular patterns, MHC major histocompatibility complex, APC- antigen presenting cell, and T helper cell)

Answer 1

The dendritic cell acquired its name because it is covered with a maze of long membrane extension that resemble the dendrites of nerve cells. Dndritic cells can be difficult to isolate because the conventional procedures for cell isolation tend to damage their long extension.

Most dendritic cells process and present antigen to th cells. For example: Langerhans cells, Interstitial dendritic cells, Interdigitating dendritic cells, Circulating dendritic cells.

The dendritic cells in different locations have different forms and function. Despite their differences,all of these dendritic cells express high level of both class II MHC molecules and members of co-stimulatory B7 family. For this reason they are more potent at an antigen presenting cells than macrophages and B-cells, both of which need to be activated before they can function as antigen presenting cells. After capturing antigen and tissues by phagocytosis dendritic cells(DC) migrate into blood and circulate to various lymphoid organ where they present antigen to T-lymphocytes.

DC descend from heamoto poetic stem cells through myeloid lineage. In one pathway a DC develops from a myeloid precursor in bone marrow then appears in blood as an immature cell that completes its differentiation in the tissues. An alternative model proposes that a late monocytic stage cell differenentiate in tissues to generate either a macrophage or DC.

THE ABOVE EXPLAINATION IS FOR SECOND LINE OF DEFENCE.

Follicular DC do not express class II MHC and therefore cannot function as antigen presenting cells for TH cell activation. Although they donot express Class II molecules follicular DC express high levels of membrane receptors for antibody and compliment. Binding of circulating antibody-antigen complexes by these receptors is thought to facilitate B cell activation in lymph nodes. These complexes have been shown to be retained on the dendritic cell membrane for very long period of time ranging from weeks to months or possibly even longer. The presence of this complex on the membrane of follicular DC is thought to play a role in development of memory B-cells within the follicle.

THE ABOVE EXPLAINATION WAS FOR THE THIRD LINE OF DEFENCE.