Why is chronic Lyme borreliosis chronic?

 Clin Infect Dis. 1997 Jul;25 Suppl 1:S64-70.Why is chronic Lyme borreliosis chronic? 
Aberer E, Koszik F, Silberer M. 
Department of Dermatology, University of Graz Medical School, Austria.
Chronic Lyme borreliosis, CLB, can present not only in different organs but also in different 
patterns. Although many theories exist about the mechanisms leading to CLB, it is known 
that viable Borrelia burgdorferi can persist for decades and cause late skin manifestations of 
acrodermatitis chronica atrophicans, ACA. Thus, the immunopathogenetic findings in ACA 
can serve as a model for studying the chronic course of Lyme borreliosis. Recent findings indicate 
that the most important cell for antigen presentation, the epidermal Langerhans cell, LC, is 
invaded by B. burgdorferi in early Lyme borreliosis. Therefore, LCs were stained 
immunohistochemically with different markers to investigate their functional activity. Numbers 
of CD1a+ LCs were reduced in erythema migrans but normal or slightly elevated in ACA. In both 
diseases there was also a marked downregulation of major histocompatibility complex class II 
molecules on LCs, as measured by staining of human leukocyte antigen DR.This phenomenon 
might be a mechanism that protects against the presentation of autoantigens and may be the 
cause of the impaired capacity of LCs to eliminate B. burgdorferi antigens, thus explaining 
why CLB is chronic

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