Natural IgM antibodies: the orphaned molecules in immune surveillance.

Natural IgM antibodies are typical victims of prejudices which originated in the mid 80 s. Over the years, these molecules were considered as the pariahs among the immune competent molecules and their characteristic properties, like low affinity, cross-reactivity and pentameric structure, were assessed as useless, difficult, nebulous, etc. Today, mainly based on a few scientists' persistent work and the key discoveries on innate immune recognition, natural IgM antibodies are "back on stage". Their role in the immune response against bacteria, viruses, fungi and possibly modified self-components as well as in therapy and diagnosis of malignancies is accepted. All the so far negatively judged features are seen in a different light, e.g. low affinity seems to be good for function and does not exclude specificity, and cross-reactivity is no longer judged as unspecific, but instead as a very economic way of immune recognition. And at last, with the use of natural IgM antibodies, a new field of tumor-specific targets has been encountered, the carbo-neo-epitopes. Therefore, by having learned from nature, the renaissance of natural IgM antibodies opens a new area of cancer therapeutics and diagnostics.