The Ecology of Humans (7-21) B Cells

 B Cells

Long-term protection against infectious diseases requires the production of highly potent antibodies by B cells. ~ English immunologist Katelyn Spillane

B cells are white blood cells (plasma cells). The role of B cells is to produce antibodies that bind to antigens.

Antibodies can take 2 physical forms. One is soluble: secreted by a B cell, floating freely in blood plasma. This type of antibody attaches to any correspondent antigen that it finds and calls for help.

Depending on the antigen, the binding may impede the disease-causing agent. Regardless, macrophages respond to the altercation.

Soluble antibodies are good for mopping up, but they don’t provide for an ongoing war against an infection. Thus, the other type of antibody binds to the surface of a B cell and alerts its owner once it comes into contact with an antigen.

B cell responses start when they encounter foreign antigens on the surfaces of a type of immune cell called antigen-presenting cells. The B cell and the antigen-presenting cell form a tight contact, known as an immune synapse, from which the B cell can acquire the antigen for processing and presentation to helper T cells so it can be destroyed. ~ Katelyn Spillane

Antigen recognition has at least 3 aspects: physical shape congruence, electrical attraction, and lipophilic interaction (chemical bonding of cell membranes).

Once activated, a B cell literally rips an antigen off the cell to which it is attached. This physical encounter allows the B cell to better sensitize itself to the antigen, and so produce more potent antibodies. If physical force does not work, the B cell employs an enzyme to peel the antigen off.

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When a B encounters an antigen, it usually is not completely activated by it. Full B activation typically requires an assist from a helper T.

In certain situations, B cells may activate themselves to produce antibodies without T help by using a pattern match between a B-cell pattern recognition receptor (PRR) and a pathogen-associated molecular pattern (PAMP). This T-less antibody activation is much faster, but also somewhat indiscriminate, as it does not represent activation by a specific antigen.

Any and all B lymphocytes contacting these PAMPs via their PRRs will start their antibody factory, regardless of whether those particular antibodies are needed to fight the infection. This can be wasteful, but the urgent response may make the difference in the body gaining a quick upper hand on an infection.

B solo initiatives are not necessarily productive, so self-activated B cells do not go on to be memory cells. Such an episode is forgotten.