Hemophagocytic lymphohistiocytosis (HLH)

Hemophagocytic lymphohistiocytosis (HLH) or hemophagocytic syndrome has increased destruction of red and white blood cells as its major hallmark. Fever, splenomegaly, jaundice, lymphocytosis and histiocytosis are the most usual symptoms and findings in this syndrome.

HLH can be either primary or secondary. Secondary refers to the acquired form and is the form that will be described here.

Evidence of infectious cause

Several findings link the syndrome to infections:

  • The immune system is activated. High levels of serum TNF-α, interleukins, IFN-γ have been found in HLH patients.1) The actual hemophagocytosis is undertaken by macrophages.
  • HLH has been associated with the following microbes: Epstein-Barr virus,2) Salmonella thyphi,3) Herpes simplex virus 1,4) HHV-6,5) Mycobacterium tuberculosis6) and other infectious agents.7)
  • Treatment of infections can reduce hemophagocytosis.8)

Possible mechanism for hemophagocytosis

The actual hemophagocytosis may be viewed as a result of overstimulated macrophages. While blood cells may harbour infectious agents and therefore the infected individual could benefit from the macrophages attacking the blood cells, there is also the possibility that hemophagocytosis benefits the infectious agent. Bacteria in hemophagocytic macrophages could access nutrients from the ingested cells, or hemophagocytic macrophages could reduce bacteria-killing activity by killing the very cells that could attack them. Yet, other macrophages could still be sufficiently activated to generate additional hemophagocytic macrophages.9)

Relation to chronic infection

The significance of hemophagocytosis in chronic L-formDifficult-to-culture bacteria that lack a cell wall and are not detectable by traditional culturing processes. Sometimes referred to as cell wall deficient bacteria. disease is not well characterized.

===== Notes and comments =====

So far, so good, Inge. Note the syntax for references. — Paul Albert 07.15.2010

===== References =====

1) , 7)
Fisman DN. Hemophagocytic syndromes and infection. Emerg Infect Dis. 2000 Nov-Dec;6(6):601-8. doi: 10.3201/eid0606.000608.
[PMID: 11076718] [PMCID: 2640913] [DOI: 10.3201/eid0606.000608]
2) , 4) , 8)
Fox CP, Shannon-Lowe C, Gothard P, Kishore B, Neilson J, O'Connor N, Rowe M. Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis in adults characterized by high viral genome load within circulating natural killer cells. Clin Infect Dis. 2010 Jul 1;51(1):66-9. doi: 10.1086/653424.
[PMID: 20504238] [DOI: 10.1086/653424]
Chien YH, Lee PI, Huang LM, Lee CY, Lin DT, Lin KH. Typhoid fever presenting as infection-associated hemophagocytic syndrome: report of one case. Acta Paediatr Taiwan. 1999 Sep-Oct;40(5):339-40.
[PMID: 10910545]
Marabelle A, Bergeron C, Billaud G, Mekki Y, Girard S. Hemophagocytic syndrome revealing primary HHV-6 infection. J Pediatr. 2010 Sep;157(3):511. doi: 10.1016/j.jpeds.2010.02.064. Epub 2010 Apr 18.
[PMID: 20400100] [DOI: 10.1016/j.jpeds.2010.02.064]
Balkis MM, Bazzi L, Taher A, Salem Z, Uthman I, Kanj N, Boulos FI, Kanj SS. Severe hemophagocytic syndrome developing after treatment initiation for disseminated Mycobacterium tuberculosis: case report and literature review. Scand J Infect Dis. 2009;41(6-7):535-7. doi: 10.1080/00365540902978075.
[PMID: 19449255] [DOI: 10.1080/00365540902978075]
Nix RN, Altschuler SE, Henson PM, Detweiler CS. Hemophagocytic macrophages harbor Salmonella enterica during persistent infection. PLoS Pathog. 2007 Dec;3(12):e193. doi: 10.1371/journal.ppat.0030193.
[PMID: 18085823] [PMCID: 2134957] [DOI: 10.1371/journal.ppat.0030193]
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