Congenital or acquired cellular deficiencies in humans have the potential to reveal much about normal hematopoiesis and immune function. We show that a recently described syndrome of monocytopenia, B and NK lymphoid deficiency additionally includes the near absence of dendritic cells. Four subjects showed severe depletion of the peripheral blood HLA-DR⁺ lineage⁻ compartment, with virtually no CD123⁺ or CD11c⁺ dendritic cells (DCs) and very few CD14⁺ or CD16⁺ monocytes. The only remaining HLA-DR⁺ lineage⁻ cells were circulating CD34⁺ progenitor cells. Dermal CD14⁺ and CD1a⁺ DC were also absent, consistent with their dependence on blood-derived precursors. In contrast, epidermal Langerhans cells and tissue macrophages were largely preserved. Combined loss of peripheral DCs, monocytes, and B and NK lymphocytes was mirrored in the bone marrow by complete absence of multilymphoid progenitors and depletion of granulocyte-macrophage progenitors. Depletion of the HLA-DR⁺ peripheral blood compartment was associated with elevated serum fms-like tyrosine kinase ligand and reduced circulating CD4⁺CD25^hiFoxP3⁺ T cells, supporting a role for DC in T reg cell homeostasis.

Both innate and adaptive immune responses are dependent on activation of nuclear factor κB (NF-κB), induced upon binding of pathogen-associated molecular patterns to Toll-like receptors (TLRs). In murine models, defects in NF-κB pathway are often lethal and viable knockout mice have severe immune defects. Similarly, defects in the human NF-κB pathway described to date lead to severe clinical disease. Here, we describe a patient with a hyper immunoglobulin M–like immunodeficiency syndrome and ectodermal dysplasia. Monocytes did not produce interleukin 12p40 upon stimulation with various TLR stimuli and nuclear translocation of NF-κB was impaired. T cell receptor–mediated proliferation was also impaired. A heterozygous mutation was found at serine 32 in IκBα. Interestingly, his father has the same mutation but displays complex mosaicism. He does not display features of ectodermal dysplasia and did not suffer from serious infections with the exception of a relapsing Salmonella typhimurium infection. His monocyte function was impaired, whereas T cell function was relatively normal. Consistent with this, his T cells almost exclusively displayed the wild-type allele, whereas both alleles were present in his monocytes. We propose that the T and B cell compartment of the mosaic father arose as a result of selection of wild-type cells and that this underlies the widely different clinical phenotype.