Molecular biology and immunology for clinicians 17: T-cell signal transduction

Basic science for the clinician 31: CD molecules of relevance to immunity, inflammation, and rheumatologic syndromes

Molecular biologic technology has allowed us to study some of the many proteins expressed by leukocytes at different stages of differentiation, activation, and proliferation. Being able to purify cells with 1 or more surface molecules (eg, by FACS or lysis) with monoclonal antibodies and complement and identifying changes as cells are stimulated or activated has given us real insights into what is happening and how we might be able to modify cells that are going astray (eg, malignancy, autoimmunity). Over the years, there has been remarkable cooperation between laboratories to bring order out of chaos; by trading reagents, scientists have been able to identify the molecules being identified by different laboratories and come up with standardized names, often within the CD, or "clusters of differentiation," framework. These names are not acronyms, and the function and role of the molecule bearing a certain CD designation is not apparent. Worse, the proliferation of numbered CD molecules (over 250, with more to come after another conference in 2004) makes interpretation of the literature very difficult for those not immersed in the field. Thus, I have chosen (nearly arbitrarily and often based on my own interests) a number of CD molecules to briefly describe, pointing out the clinical relevance of each. It is worth reflecting on the fact that many of these were discussed in previous contributions to this series (as is pointed out in the following article). For those of you with the fortitude to follow this series, see how far you (and all of science) have come!

Basic science for the clinician 38: B cells, factories, and immunomodulators

In a previous article in this series, we explored how developing pre-T cells learn how to be well-behaved T cells that recognize and honor the "self versus nonself" dichotomy of the universe. B cells do much of the same sort of thing, with multipotent stem cells becoming committed to ultimately becoming B cells within the bone marrow and then, after judicious culling of the flock, going off to the spleen to learn the final lessons needed to become "well-behaved" B cells. Like with T cells, there are a large number of things that can, and do, go wrong. If there is a failure of the system and B cells do not develop properly, hypogammaglobulinemia may develop as a result of a number of immune deficiency syndromes that can be quite devastating. If autoreactive cells survive to emerge into the periphery, autoimmunity, either organ-specific or more global, may occur. If B cells in the periphery proliferate in an uncontrolled fashion, a variety of B cell lymphoproliferative syndromes may develop, recognizable by the phenotypic markers of their originating B cell lineage level of differentiation. The full details of how autoreactive B cells survive and thrive, only to cause disease, are not yet clear, but identification of many of the phenotypic surface markers and circulating growth factors identified to this point have borne therapeutic fruit.