B-Cells and antibodies

B cells are specialized immune cells that can detect virtually any kind of pathogen and produce millions of antibodies. When a B cell detects a pathogen, it will then evolve into a plasma (producing antibodies) or memory cell (recording the pathogen for future attacks)

Schematic of B cell differentiation (usually a little more complicated than this), B cells (naive)  creates antibodies at their surface, they become activated when a specific antigen (it can be a virus, a bacteria, or another unidentified particle, here exemplified as the green star), gets recognized by the antibody. With the help of other cells (T helper cells), they can evolve into plasma B cells (producing millions of antibodies, with a shorter life span) or a memory cell (a cell that remembers the type and specificities of the antigen, but with a longer life span)

How science uses antibodies?
Because of their ability to detect only one specific biomolecule, antibodies are often viewed as the best way to interact with biosensors.

A strategy to mass produce them is the Hybridoma technology (developed in 1975 by Milstein, and Köhler). Briefly, a plasma B cell is fused together with a cancer cell, in this way, the plasma B cell does not die and will keep on producing millions of specific antibodies. [1]

A simplified overview of an antibody(IgG), showing the principal structures. In human bodies, they can conjugate with antigens and facilitate macrophage eating. It also can initiate lysis in cooperation with the complement attack complex

Antibodies work well with ELISA (Enzyme Linked Immuno Sorbent Assay) where the antibodies detect a specific antigen and they are linked next with a fluoro-enzyme(an enzyme capable of emitting light), a deep analysis on a microscope will yield the response, if everything goes well, the assay will be as bright as a field of fireflies.

Antibodies have been also used in cantilevers or membranes (MEMS) to detect by weight the presence of a given antigen. [2] The detection strategy in this case, can be optical, piezoelectric, or even by capacitance.

Cantilever with antibodies, based on the size and weight, the cantilever can deflect downside or even upside as seen on [3] (with SCFV instead of antibodies)

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[1] Human antibodies by design, Vaughan, T. J, Osbourn, J. K, Tempest, P. R, Nature biotechnology, 16, 535-539 (1998)
[2] Cantilever transducers as a platform for chemical and biological sensors, Lavrik. N. V, Sepaniak, M. J, Datskos P. G, Review of scientific instruments, 75, 2220-2253 (2004)
[3] A label-free immunosensors array using single-chain antibody fragments, Backmann N, Zahnd C, Huber F, Bietsch A, Plückthun A, Lang H. P, Güntherodt H. J, Hegner M, Gerber C, PNAS, 102, 14587-14592 (2005)