Insights into lymphocyte development from X-linked immune deficiencies.

The genetic immune deficiencies have drawn the attention of physicians and immunologists for more than 40 years. The selectivity of these deficiencies brings into focus the contribution of the response of each arm of the immune system to specific pathogens. Recently, the genes underlying four X-linked defects in immune development in humans have been identified by either positional cloning or candidate-gene cloning techniques. Remarkably, these genetic defects reveal a microcosm of lymphocyte developmental controls involving cell-cell interactions, combinatorial cell surface receptor specificity and lineage-specific signal transduction.