Mechanism explains how immune cells detect threats

The immune system consists of different components. Some cells are tasked with detecting threats, such as bacteria and viruses. Others are present in the 'effector phase', which means they are supposed to eradicate the threat. The latter part is performed with cells that contain poison to kill other, infected cells with, or with cells that create antibodies which bind and neutralize whatever it is that invaded our body. We know that during the detection phase, specialized immune cells use receptors to recognize patterns that hint at foreign material. However, the mechanism that explains how they present their findings to other cells and initiate the immune response was not entirely known. A study performed by the University of British Columbia explains how invasions are flagged and how the findings are presented to effector cells.

Dendritic cells
The mechanism which explains how the immune system detects and acts on a foreign threat was found in so-called dendritic cells. They are the first line of defence in the immune system, and tasked with swallowing everything that appears to be foreign of nature. Inside the cell, various receptors are present to detect specific patterns associated with bacteria, viruses or other invaders. After the foreign material, called an antigen, is processed, a special molecule on the surface of the dendritic cell 'presents' the findings to other immune cells whereafter the response is initiated.

A dendritic cell with long 'dendrites' to capture foreign material.

CD74
At the University of British Columbia, researchers found that dendritic cells need a molecule called CD74 to correctly process the antigen and present the findings to other immune cells. Without this molecule, the detection phase breaks down, and consequently affects all of the immune system's response towards an intruder. CD74's function was found by knocking out the required gene for the molecule in mice. They found that these mice lacked the intracellular processing required to adequately present antigens.

Clinical relevance
Because CD74 enables dendritic cells to process antigens and present them to effector cells, it has an important role in initiating the immune response. The researchers from the University of British Columbia think we may be able to use this mechanism to improve the body's response against certain invaders, such as HIV. By artificially improving the detection capability of the body, pathogens could very well become less effective.

A dendritic cell communicates with a T cell to initiate the immune response. Additionally a B cell that produces antibodies is also activated.