About IgM
Immunoglobulins (Ig) are the antigen recognition molecules of B cells. An Ig molecule is made up of 2 identical heavy chains and 2 identical light chains (see MIM 147200) joined by disulfide bonds so that each heavy chain is linked to a light chain and the 2 heavy chains are linked together. Each Ig heavy chain has an N-terminal variable (V) region containing the antigen-binding site and a C-terminal constant (C) region, encoded by an individual C region gene, that determines the isotype of the antibody and provides effector or signaling functions. The heavy chain V region is encoded by 1 each of 3 types of genes: V genes (see MIM 147070), joining (J) genes (see MIM 147010), and diversity (D) genes (see MIM 146910). The C region genes are clustered downstream of the V region genes within the heavy chain locus on chromosome 14. The IGHM gene encodes the C region of the mu heavy chain, which defines the IgM isotype. Naive B cells express the transmembrane forms of IgM and IgD (see IGHD; MIM 1471770) on their surface. During an antibody response, activated B cells can switch to the expression of individual downstream heavy chain C region genes by a process of somatic recombination known as isotype switching. In addition, secreted Ig forms that act as antibodies can be produced by alternative RNA processing of the heavy chain C region sequences. Although the membrane forms of all Ig isotypes are monomeric, secreted IgM forms pentamers, and occasionally hexamers, in plasma (summary by Janeway et al., 2005).[supplied by OMIM, Aug 2010]

About PE-eFluor 610
PE-eFluor™ 610 (PE-eF610, RPE-eF610) from Thermo Fisher Scientific is an orange-emitting tandem fluorophore that combines pycoerythrin (PE) and eFluor™ 610. The donor molecule, PE can be excited by the 488-nm blue, 532-nm green, or 561-nm yellow-green laser and and transfers energy to the acceptor molecule, eF610, which emitts light that can be captured with a 610/20 nm bandpass filter. PE-eF610 has an excitation peak at 565 nm and an emission peak at 607 nm, and is suitable alternative to PE-Texas Red®. PE-eF610 is mainly used for flow cytometry. This tandem is often a great option because of PE is excitable by multiple lasers due to its broad excitation spectrum and the eFluor™ 610 acceptor molecule emits brightly in the Orange/Red spectrum. Many cytometers are commonly set up with the 610/20 bandpass filter that can detect this fluorophore's emission. This dye is part of the larger eFluor™ dye family, developed by eBioscience which is now part of ThermoFisher Scientific.