DPB remains idiopathic, which means an exact [[physiological]], [[Environment (biophysical)|environment]]al, or [[pathogen]]ic cause of the disease is unknown.<ref name=dpb06/> However, several known factors are involved with the pathogenesis of DPB.<ref name=hla98/><ref name=hla99/>
The [[major histocompatibility complex]] (MHC) is a large [[genome|genomic]] region found in most [[vertebrate]]s, that is associated with [[mating]] and the [[immune system]]. It is located on [[chromosome 6]] in humans. A subset of the human MHC is [[human leukocyte antigen]] (HLA), which controls the [[antigen presentation|antigen presenting system]], as part of [[adaptive immunity]] against [[pathogen]]s such as [[bacteria]] and [[virus]]es.
Genetic predisposition for DPB has been localized to two HLA [[haplotype]]s unique to Asians, particularly of East Asian descent.<ref name=hla98/><ref name=hla00/> [[HLA-B54]] is associated with DPB in Japanese patients,<ref name=hla98/> while [[HLA-A11]] is associated with the disease in Koreans.<ref name=hla99/> One or more [[candidate gene]]s<ref name=orf>{{cite journal |author=Matsuzaka Y, Tounai K, Denda A, Tomizawa M, Makino S, Okamoto K, Keicho N, Oka A, Kulski JK, Tamiya G, Inoko H |title=Identification of novel candidate genes in the diffuse panbronchiolitis critical region of the class I human MHC |journal=Immunogenetics |volume=54 |issue=5 |pages=301-309 |year=2002 |pmid=12185533 }}</ref> (a gene suspected to be responsible for a trait or disease) within this region of [[human leukocyte antigen|class I HLA]] are believed to be the genetic factor responsible for DPB, allowing disease susceptibility<ref name=hla00/> related to the structure of the [[antigen presentation|antigen presenting]] [[molecules]] selected by these genes.<ref name=tap>{{cite journal |author=Keicho N, Tokunaga K, Nakata K, Taguchi Y, Azuma A, Tanabe K, Matsushita M, Emi M, Ohishi N, Kudoh S |title=Contribution of TAP genes to genetic predisposition for diffuse panbronchiolitis |journal=Tissue Antigens |volume=53 |issue=4 pt. 1 |pages=366-373 |year=1999 |pmid=10323341 }}</ref>
Candidate genes within HLA that are most likely involved with DPB suceptibility include: [[FAM46A|C6orf37]]<ref name=orf/> and [[TAP2]].<ref name=tap/>
Another such gene, though not a part of the HLA system, is the gene for [[interleukin 8]] (IL-8)<ref name=il8>{{cite journal |author=Emi M, Keicho N, Tokunaga K, Katsumata H, Souma S, Nakata K, Taguchi Y, Ohishi N, Azuma A, Kudoh S |title=Association of diffuse panbronchiolitis with microsatellite polymorphisms of the human interleukin 8 (IL-8) gene |journal=J Hum Genet. |volume=44 |issue=3 |pages=169-172 |year=1999 |pmid=10319580 }}</ref>
located on [[chromosome 4]]. The role of IL-8 to produce inflammation by causing the proliferation of neutrophil granulocytes at any site of pathogenic involvement, in conjunction with strong [[microsatellite]] identification with DPB, implicates IL-8 as another candidate gene associated with DPB pathogenesis.<ref name=il8/> This also supports the idea that several factors, including those unrelated to HLA as well as non-genetic, and unknown factors, may cause the disease.<ref name=il8/>
The inflammation common to DPB also provides a means to determine other mechanisms of disease pathogenesis.<ref name=cd8>{{cite journal |author=Kadota J, Mukae H, Tomono K, Kohno S |title=High concentrations of beta-chemokines in BAL fluid of patients with diffuse panbronchiolitis |journal=Chest |volume=120 |issue=2 |pages=602-607 |year=2001 |pmid=11502665 }}</ref> This may be partly due to the persistence of inflammation in DPB, with ''or'' without the presence of the two opportunistic bacteria sometimes found with the disease (''haemophilus influenzae'', ''pseudomonas aeruginosa'').<ref name=path/> Inflammation caused by the [[chemokine]] [[CCL4|MIP-1alpha]] and its involvement with [[CD8|CD8+]] [[T-cell]]s is believed to be one such mechanism of DPB pathogenesis.<ref name=cd8/>
Other factors found with DPB play a part in its pathogenesis by sometimes causing minor variations of it.
[[Beta defensin]]s, a family of [[antimicrobial]] [[peptide]]s found in the respiratory tract, are responsible for further inflammation in DPB, when associated pathogens like ''pseudomonas aerugenosa'' are present.<ref name=def>{{cite journal |author=Hiratsuka T, Mukae H, Iiboshi H, Ashitani J, Nabeshima K, Minematsu T, Chino N, Ihi T, Kohno S, Nakazato M |title=Increased concentrations of human beta-defensins in bronchoalveolar lavage fluid of patients with diffuse panbronchiolitis |journal=Thorax |volume=58 |issue=5 |pages=425-430 |year=2003 |pmid=12728165 }}</ref>
If present in a DPB patient, the [[human T-lymphotropic virus|human T-lymphotropic virus, type I]], a [[retrovirus]], modifies DPB pathogenesis by infecting [[CD4|CD4+]] cells ([[Helper T-cell]]s) and altering there effectiveness in reducing both known and unknown pathogenic involvement with DPB.<ref name=htlv>{{cite journal |author=Yamamoto M, Matsuyama W, Oonakahara K, Watanabe M, Higashimoto I, Kawabata M, Osame M, Arimura K |title=Influence of human T lymphotropic virus type I on diffuse pan-bronchiolitis |journal=Clin Exp Immunol. |volume=136 |issue=3 |pages=513-520 |year=2004 |pmid=15147354 }}</ref> Conversely, an onset of DPB causes increased frequency of [[Adult T-cell leukemia]] in human lymphotropic virus sufferers.<ref name=htlv/>
With macrolide therapy in DPB, great reduction in bronchiolar inflammation and damage is achieved through suppression of not only neutrophil granulocyte proliferation, but also lymphocyte activity and obstructive mucus and sputum secretions in airways.[1] The antimicrobial and antibiotic effects of macrolides, however, are not believed to be involved in their beneficial effects toward treating DPB.[3] This is evident, as the treatment dosage is much too low to fight infection, and in DPB cases with the occurrence of macrolide-resistant pseudomonas aeruginosa, macrolide therapy still produces substantial anti-inflammatory results.[1]
Advanced cases of DPB, where severely excessive sputum production resistant to macrolides persists, additional therapy with the inhalant tiotropium has been shown to ease these symptoms and the related shortness of breath.[4]
↑ 1.01.11.21.3Keicho N, Kudoh S (2002). "Diffuse panbronchiolitis: role of macrolides in therapy". Am J Respir Med. 1 (2): 119–131. PMID14720066.
↑ 2.02.1Lopez-Boado YS, Rubin BK (2008). "Macrolides as immunomodulatory medications for the therapy of chronic lung diseases". Curr Opin Pharmacol. Epub ahead of print. PMID18339582.
↑Schultz MJ (2004). "Macrolide activities beyond their antimicrobial effects: macrolides in diffuse panbronchiolitis and cystic fibrosis". J Antimicrob Chemother. 54 (1): 21–28. PMID15190022.
↑Saito Y, Azuma A, Morimoto T, Fujita K, Abe S, Motegi T, Usuki J, Kudoh S (2008). "Tiotropium ameliorates symptoms in patients with chronic airway mucus hypersecretion which is resistant to macrolide therapy". Intern Med. 47 (7): 585–591. PMID18379141.CS1 maint: Multiple names: authors list (link)
