Correspondence

Toll-like Receptor 4 Polymorphisms and Aspergillosis

N Engl J Med 2009; 360:634-636February 5, 2009

Article

To the Editor:

Bochud et al. (Oct. 23 issue)1 present data suggesting an association between toll-like receptor 4 (TLR4) haplotypes in unrelated donors and an increased risk of invasive aspergillosis among recipients of allogeneic hematopoietic-cell transplants. The authors theorize that this association is due to the capacity of TLR4 to recognize ligands present on Aspergillus fumigatus.2 However, there is another possible explanation for the findings that should be considered. During much of the period of the study, transplant recipients with febrile neutropenia that was unresponsive to antibiotics received amphotericin B. This is significant because conventional and lipid formulations of amphotericin B activate phagocytic cells by stimulating toll-like receptor 2 (TLR2) and TLR4 to release proinflammatory cytokines and chemokines.3,4 These immunomodulatory properties of amphotericin B may contribute to its antifungal activity.5 Optimal efficacy of liposomal amphotericin B in mice with bone marrow transplants and aspergillosis has been linked to TLR4-mediated activation of neutrophils by amphotericin B.4 Thus, the association between donor TLR4 haplotypes and the risk of aspergillosis may be due at least in part to decreased immunostimulation of donor cells by amphotericin B.

Stuart M. Levitz, M.D.
University of Massachusetts Medical School, Worcester, MA 01605
stuart.levitz@umassmed.edu

Shmuel Shoham, M.D.
Washington Hospital Center, Washington, DC 20010

John D. Cleary, Pharm.D.
University of Mississippi Medical Center, Jackson, MS 39216

5 References

1. 1

   Bochud P-Y, Chien JW, Marr KA, et al. Toll-like receptor 4 polymorphisms and aspergillosis in stem-cell transplantation. N Engl J Med 2008;359:1766-1777
   Full Text | Web of Science | Medline

2. 2

   Mambula SS, Sau K, Henneke P, Golenbock DT, Levitz SM. Toll-like receptor (TLR) signaling in response to Aspergillus fumigatus. J Biol Chem 2002;277:39320-39326
   CrossRef | Web of Science | Medline

3. 3

   Sau K, Mambula SS, Latz E, Henneke P, Golenbock DT, Levitz SM. The antifungal drug amphotericin B promotes inflammatory cytokine release by a Toll-like receptor- and CD14-dependent mechanism. J Biol Chem 2003;278:37561-37568
   CrossRef | Web of Science | Medline

4. 4

   Bellocchio S, Gaziano R, Bozza S, et al. Liposomal amphotericin B activates antifungal resistance with reduced toxicity by diverting Toll-like receptor signalling from TLR-2 to TLR-4. J Antimicrob Chemother 2005;55:214-222
   CrossRef | Web of Science | Medline

5. 5

   Rogers PD, Pearson MM, Cleary JD, Sullivan DC, Chapman SW. Differential expression of genes encoding immunomodulatory proteins in response to amphotericin B in human mononuclear cells identified by cDNA microarray analysis. J Antimicrob Chemother 2002;50:811-817
   CrossRef | Web of Science | Medline

To the Editor:

Bochud and colleagues demonstrate an important association of TLR4 polymorphisms with aspergillosis after allogeneic stem-cell transplantation. As the authors point out, TLR4 polymorphisms might be associated with other risk factors for aspergillosis. Cytomegalovirus (CMV) disease is strongly and independently associated with aspergillosis. In a recent large study of stem-cell transplant recipients, patients with CMV disease had the highest overall hazard ratio for aspergillosis (6.9), and the hazard ratio was higher with an early onset of CMV disease than with a late onset.1 Although TLR4 does not seem to be directly involved in the recognition of CMV, TLR4 ligands enhance the ability of dendritic cells to present CMV antigen, resulting in an increased number of antigen-specific CD4+ and CD8+ cells.2 Two studies have shown an association of TLR4 polymorphisms with CMV disease after renal transplantation.3,4 Therefore, CMV could be an intermediate variable in the association of TLR4 polymorphisms with aspergillosis, and it may be questionable to consider it as a confounding factor in a regression model. The important findings reported by Bochud and colleagues would be strengthened by an analysis of the association between TLR4 polymorphisms and CMV disease.

Carlos Cervera, M.D.
Asuncion Moreno, Ph.D.
Francisco Lozano, Ph.D.
Hospital Clinic of Barcelona, 08023 Barcelona, Spain
ccervera@clinic.ub.es

4 References

1. 1

   Garcia-Vidal C, Upton A, Kirby KA, Marr KA. Epidemiology of invasive mold infections in allogeneic stem cell transplant recipients: biological risk factors for infection according to time after transplantation. Clin Infect Dis 2008;47:1041-1050
   CrossRef | Web of Science | Medline

2. 2

   Lore K, Betts MR, Brenchley JM, et al. Toll-like receptor ligands modulate dendritic cells to augment cytomegalovirus- and HIV-1-specific T cell responses. J Immunol 2003;171:4320-4328
   Web of Science | Medline

3. 3

   Cervera C, Lozano F, Saval N, et al. The influence of innate immunity gene receptors polymorphisms in renal transplant infections. Transplantation 2007;83:1493-1500
   CrossRef | Web of Science | Medline

4. 4

   Ducloux D, Deschamps M, Yannaraki M, et al. Relevance of Toll-like receptor-4 polymorphisms in renal transplantation. Kidney Int 2005;67:2454-2461
   CrossRef | Web of Science | Medline

To the Editor:

The single-nucleotide polymorphism in the third exon of human TLR4 (Asp299Gly) and the cosegregating missense mutation at amino acid 399 (Thr399Ire), which correspond to the extracellular domain of TLR4, have different distributions in different populations. Whereas 5 to 20% of persons in white populations bear these cosegregating TLR4 polymorphisms, they are virtually missing in Asian populations.1 Nonetheless, severe invasive aspergillosis develops in many patients undergoing allogeneic hematopoietic stem-cell transplantation in Japan,2 which raises a question regarding the extent to which the risk of invasive aspergillosis among patients undergoing allogeneic hematopoietic stem-cell transplantation is attributable to the donor haplotype of these mutations. To prove their hypothesis, Bochud et al. must present, in addition to their epidemiologic results, direct evidence that the cells of the immune system bearing these mutations are actually hyporesponsive to aspergillus antigens.3

Yusuke Asakura, M.D., Ph.D.
Toru Komatsu, M.D., Ph.D.
Aichi Medical University, Aichi 480-1195, Japan
yasakura@aichi-med-u.ac.jp

3 References

1. 1

   Ferwerda B, McCall MB, Alonso S, et al. TLR4 polymorphism, infectious diseases, and evolutionary pressure during migration of modern humans. Proc Natl Acad Sci U S A 2007;104:16645-16650
   CrossRef | Web of Science | Medline

2. 2

   Yamasaki S, Heike Y, Mori S, et al. Infectious complications in chronic graft-versus-host disease: a retrospective study of 145 recipients of allogeneic hematopoietic stem cell transplantation with reduced- and conventional-intensity conditioning regimens. Transpl Infect Dis 2008;10:252-259
   CrossRef | Web of Science | Medline

3. 3

   Arbour NC, Lorenz E, Schutte BC, et al. TLR4 mutations are associated with endotoxin hyporesponsiveness in humans. Nat Genet 2000;25:187-191
   CrossRef | Web of Science | Medline

Author/Editor Response

Levitz et al. hypothesize that the association between donor TLR4 Asp299Gly and the risk of aspergillosis may be due to decreased immunostimulation of donor cells by amphotericin B. This hypothesis is not supported by a recent study by Carvalho et al., which linked the Asp299Gly polymorphism to chronic cavitary aspergillosis.1 Unlike patients undergoing hematopoietic-cell transplantation, patients in whom chronic cavitary aspergillosis develops usually do not receive amphotericin B before the diagnosis of fungal infection is made. Thus, it is most likely that polymorphisms in TLR4 can influence susceptibility to aspergillosis in a manner that is independent of administered amphotericin B.

Cervera et al. suggest that the TLR4 Asp299Gly may be associated with CMV disease, which would in turn lead to increased susceptibility to invasive aspergillosis. This hypothesis is not supported by the multivariate analysis performed in our validation study, which included CMV disease as a covariate and identified the TLR4 polymorphisms as an independent risk factor for invasive aspergillosis. Also, the association between Asp299Gly and chronic cavitary aspergillosis suggests that there may be a more direct association with diseases caused by aspergillus species.1 Although an association between TLR4 polymorphisms and CMV disease cannot be ruled out, this study suggests that TLR4 polymorphisms influence susceptibility to aspergillosis in a manner that is independent of CMV disease.

The role of ethnicity in susceptibility to infections is an interesting topic, as raised by Asakura and Komatsu. In contrast to primary immunodeficiencies, which typically involve a single, rare polymorphism, leading to important functional consequences, susceptibility to infections in the general population is usually considered to result from variants in several genes, each leading to smaller functional alterations. Results of in vitro and ex vivo studies have shown that innate immune recognition of fungal pathogens is mediated by several receptors — a finding that is not surprising, given the complicated cell-wall architecture of fungi.2 In a Korean population, a haplotype in the interleukin-10 gene (IL-10) was reported to influence susceptibility to invasive aspergillosis3; also, a recent study identified a polymorphism in the host plasminogen gene that was associated with a risk of invasive aspergillosis.4 Thus, we believe that inherited risks are likely to be multifactorial and to differ among specific ethnic groups, with polymorphisms in genes other than TLR4 also influencing susceptibility to invasive infection and airway disease.

Pierre-Yves Bochud, M.D.
Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland

Kieren A. Marr, M.D., Ph.D.
Johns Hopkins University, Baltimore, MD 21205

Michael Boeckh, M.D.
Fred Hutchinson Cancer Research Center, Seattle, WA 98109
mboeckh@fhcrc.org

4 References

1. 1

   Carvalho A, Pasqualotto AC, Pitzurra L, Romani L, Denning DW, Rodrigues F. Polymorphisms in toll-like receptor genes and susceptibility to pulmonary aspergillosis. J Infect Dis 2008;197:618-621
   CrossRef | Web of Science | Medline

2. 2

   Netea MG, Brown GD, Kullberg BJ, Gow NA. An integrated model of the recognition of Candida albicans by the innate immune system. Nat Rev Microbiol 2008;6:67-78
   CrossRef | Web of Science | Medline

3. 3

   Seo KW, Kim DH, Sohn SK, et al. Protective role of interleukin-10 promoter gene polymorphism in the pathogenesis of invasive pulmonary aspergillosis after allogeneic stem cell transplantation. Bone Marrow Transplant 2005;36:1089-1095
   CrossRef | Web of Science | Medline

4. 4

   Zaas AK, Liao G, Chien JW, et al. Plasminogen alleles influence susceptibility to invasive aspergillosis. PLoS Genet 2008;4:e1000101-e1000101
   CrossRef | Web of Science | Medline

Citing Articles (5)

Citing Articles

1. 1

   Michael Ok, Hermann Einsele, Juergen Loeffler. (2011) Genetic susceptibility to Aspergillus fumigatus infections. International Journal of Medical Microbiology 301:5, 445-452
   CrossRef

2. 2

   Frédéric Lamoth, Ivana Rubino, Pierre-Yves Bochud. (2011) Immunogenetics of invasive aspergillosis. Medical Mycology 49:S1, S125-S136
   CrossRef

3. 3

   Cristina Cunha, Franco Aversa, Giovanni Bistoni, Andrea Casagrande, Fernando Rodrigues, Luigina Romani, Agostinho Carvalho. (2011) Immunogenetic Profiling to Predict Risk of Invasive Fungal Diseases: Where Are We Now?. Immunological Investigations 40:7-8, 723-734
   CrossRef

4. 4

   Markus Mezger, Hermann Einsele, Juergen Loeffler. (2010) Genetic susceptibility to infections with Aspergillus fumigatus. Critical Reviews in Microbiology 36:2, 168-177
   CrossRef

5. 5

   Stuart M. Levitz. (2009) Genetic factors associated with susceptibility to invasive aspergillosis. Current Fungal Infection Reports 3:3, 129-130
   CrossRef