Guz and Pontet - Figure 4
A case of monoclonal IgAlambda, properly typed by IEP but for which it has been impossible
to identify the bound light chains by IF: while the same anti-bound and free lambda
antiserum has been evaluated as a good reagent in IEP, it cannot react in IF.
Prot. means total protein concentration; antisera are mentioned on the left; tested
sera are mentioned on the right; other symbols and abbreviations have been previously
Free light chains: these are isolated light chains, unbound to heavy chains, with a
relative molecular mass Mr╩┼╩(22╩500)n , according to their polymerisation degree;
they are undetectable by usual techniques in biological fluids of a normal individual.
Of the kappa or lambda type, they can be specifically identified by anti-kappa or
lambda free light chain labeled antisera. Their historical name of Bence Jones proteins,
given at a time when techniques and molecular concepts were very different from what they
are now, should be avoided (3), because it generates too much confusion in prescriptions,
biological fluids, techniques, relative molecular mass and polyclonal/monoclonal aspects.
Bound and free light chains: these are constituted by both free light chains, above
defined, and heavy chain bound light chains, those which are normally included in the
Ig four chain molecule. They, as a whole, are recognized by anti-bound and free kappa
or lambda labeled antisera, owing to the presence of so-called conformational antigenic
sites, that is to say that their identity is determined by the quaternary structure
related space configuration of the molecules.
Specificity: the specificity of an antibody is its capacity to distinguish various close
structured antigenic determinants, binding them with a different affinity. The most
important is the affinity difference of an antibody for two given antigens, the highest
will be the specificity of the antibody for the antigen towards which it shows the
strongest affinity. The ideal specificity corresponds to a maximum affinity for the
considered antigen and to a zero affinity for all other antigens. The specificity of
an antibody is directly correlated to the stability of the antigen-antibody complex
obtained, a high specificity corresponding to a low dissociation speed constant.
The specificity of an antiserum is determined by that of the antibodies it contains.
If it contains one specific antibody, the antiserum is monospecific, if it contains two,
it is bispecific etc╔An immunological reaction specificity is determined by the
specificity of the involved antiserum (and by that of the antibody included).
Antibody specificity and valence should not be confused.
Type: this word points out variants of nonallotypic nature defined by the Ig light chain
constant regions (CL). Thus the word typing should be strictly used to talk about the
determination of Ig light chain type. Determining the heavy chain of Ig refers to the
class or subclass of it. To assert the existence of a monoclonal Ig in a biological
fluid, we need to determine the whole isotype, thus both class and type. The word
isotyping is not quite of a current use.
Valence: the valence of an antibody is the number of specific sites, or paratopes,
carried by the N terminal end of Ig and structurally determined by Ig VH and VL regions.
To be functional, an antibody must be at least bivalent, that is to say bearing two
Fab fragments. This word should not be confused with the word specificity.