A variant of myelokathexis with hypogammaglobulinemia: lymphocytes as well as neutrophils may reverse in response to infections

Oligoclonality, impaired class switch and B-cell memory responses in WHIM syndrome

Heterozygous truncating mutations in CXCR4 have been identified as a cause of WHIM syndrome (warts, hypogammaglobulinemia, immunodeficiency and myelokathexis). The receptor truncations have been proposed to lead to altered lymphocyte trafficking. The purpose of the described studies was to characterize the B-cell repertoire in WHIM subjects. We confirmed profound B-cell lymphopenia and demonstrated oligoclonality of the circulating B-cell pool by HCDR3 spectratyping. The response to immunization was studied in one subject utilizing a bacteriophage PhiX174 immunization protocol. Spectratyping showed oligoclonality at baseline with normalization of the HCDR3 length distribution by 5 months after immunization with PhiX174 with eventual return to the baseline state. Isotype switching from phage specific neutralizing antibody of the IgM class to IgG was markedly reduced. Overall, these data suggest that impaired CXCR4 signaling in WHIM syndrome results in defective B-cell function and abnormal isotype switching, possibly through effects on germinal center trafficking of lymphocytes.

WHIM syndrome: congenital immune deficiency disease

PURPOSE OF REVIEW

Warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is characterized by susceptibility to human papilloma virus infection-induced warts and carcinomas; neutropenia, B-cell lymphopenia and hypogammaglobulinema-related infections; and bone marrow myelokathexis (myeloid hyperplasia with apoptosis). The purpose of this report is to review new findings about WHIM.

RECENT FINDINGS

Most WHIM patients have heterozygous C-terminus deletion mutations of the intracellular carboxy terminus of the chemokine receptor CXCR4. WHIM leukocytes have enhanced responses to CXCL12, the cognate ligand of CXCR4. Enhanced activity of CXCR4 delays release of mature neutrophils from bone marrow, resulting in neutropenia and apoptosis of mature neutrophils retained in the marrow. Finding two patients with WHIM who do not have detectable mutations of CXCR4 but whose cells are hyperresponsive to CXCL12 raises the possibility that there is more than one genetic basis for WHIM. One patient had low levels of G-protein receptor kinase 3, and the functional hyperactivity response to CXCL12 was corrected by forced gene transfer-mediated overexpression of G-protein receptor kinase 3, implicating defects in function of this protein as a potential alternate genetic cause of WHIM.

SUMMARY

Subjects reviewed include clinical presentation, diagnosis, and treatment of WHIM and advances in understanding the genetic basis of WHIM.

WHIM syndrome

A WHIM-szindróma ritka, autoszomális domináns öröklődésmenetű primer immunhiány-betegség, amelyre vírusos szemölcsök, hypogammaglobulinaemia, visszatérő fertőzések és myelokathexis jellemző. A közleményben a szerzők egy esetismertetés kapcsán mutatják be a betegség klinikumát, laboratóriumi eltéréseit, összefoglalják a kórkép molekuláris patomechanizmusával kapcsolatos ismereteket és kezelésének lehetőségeit. A szerzők szerint a betegség inkomplett megjelenése a késői felismerés és kezelés gyakori oka gyermekkorban.

WHIM syndrome: a defect in CXCR4 signaling

The study of inherited immunodeficiencies has proven valuable in elucidating molecular signaling cascades underlying the developmental and functional regulation of the human immune system. The first example of a human immunologic disease caused by mutation of a chemokine receptor was provided by WHIM (warts, hypogammaglobulinemia, infections, and myelokathexis) syndrome, a rare, combined immunodeficiency featuring an unusual form of neutropenia. Subsequent studies following the initial description of mutations in the CXCR4 gene have revealed a striking concordance in the types of mutations observed, suggesting that impaired regulation of receptor signaling by truncation of the cytoplasmic tail domain is an essential aspect in disease pathogenesis. Biochemical studies have provided support for the model that impaired receptor downregulation leads to the characteristic immunologic and hematologic disturbances. Interestingly, these genetic studies have also identified phenocopies with the same clinical features but without mutation of CXCR4, suggesting that mutations in as yet uncharacterized downstream regulators of the receptor may be involved in a proportion of cases.

CXCR4 mutations in WHIM syndrome: a misguided immune system?

Chemokines and their receptors are key molecules in the development and function of immune cell populations and the organization of lymphoid organs. Despite their central role in immunologic function, genetic studies exploring the intersection of chemokines or their receptors and human health have revealed few associations of unambiguous significance. The best-characterized examples have revealed striking selective advantage conferred by loss of receptors used as portals of entry by pathogens. Recently, mutations in the CXCR4 chemokine receptor gene were identified in a dominantly inherited immunodeficiency disease, WHIM syndrome. Genetic and biochemical evidences suggest that the loss of the receptor cytoplasmic tail domain results in aberrant signaling. Analyses of mutant cell responses to the receptor ligand CXCL12 have revealed enhanced chemotaxis, confirming the gain-of-function effect of the truncation mutations. The clinical features and potential mechanism of immunodeficiency in WHIM syndrome patients are discussed in this review.

WHIM syndrome: a genetic disorder of leukocyte trafficking

PURPOSE OF REVIEW

WHIM syndrome (the association of warts, hypogammaglobulinemia, recurrent bacterial infections, and 'myelokathexis') is a rare congenital form of neutropenia associated with an unusual immune disorder involving hypogammaglonulinemia and abnormal susceptibility to warts. In this review, we describe the clinical, laboratory and genetic features of WHIM syndrome.

RECENT FINDINGS

The identification of chemokine receptor CXCR4 as the causative gene of WHIM syndrome yields new interest in the study of this disease as a model for the comprehension of CXCR4 biology in humans and highlights the importance of the chemokine network for inducing effective immune responses and governing leukocyte trafficking.

SUMMARY

CXCR4 participates in several biological processes (bone marrow hematopoiesis, cardiogenesis, angiogenesis, neurogenesis) and is implicated in different clinical pathologic conditions (WHIM, HIV infection, tumor metastatization, autoimmunity). Pharmacologic agents that modulate CXCR4 expression/function are already available and promise a wide range of future clinical applications.

Infections in patients with inherited defects in phagocytic function

Patients with defects in phagocytic function are predisposed to intracellular microorganisms and typically have early dissemination of the infection. Recognition of the underlying disorder and aggressive antimicrobial therapy has been beneficial for the patients. Improved understanding of the pathophysiology has also affected patient management by allowing specific, targeted immunomodulatory intervention. The disorders described in this review are not common but have had a significant impact on our understanding of the role of phagocytic cells in host defense. Conversely, understanding the role of the neutrophil and macrophage in infection has benefited not just the patients described in this review but also other patients with similar disease processes.