Axenically grown Entamoeba histolytica produces a pentapeptide (
Met-Gln-Cys-Asn-Ser) with several anti-inflammatory properties, including the inhibition of human monocyte locomotion (
Monocyte Locomotion Inhibitory Factor (
MLIF)). A construct displays the same effects as the native material. It remains to be seen if
MLIF is used, or even produced in vivo by the tissue-invading parasite. If
MLIF were to be relevant in invasive
amoebiasis, immunizing against it could diminish this parasite advantage and prevent lesions. KLH-linked
MLIF mixed with
Freund's adjuvant was too aggressive an immunizing material to answer this question. However, immunization with a tetramer of
MLIF (but not a scrambled version of
MLIF) around a
lysine core (
MLIF-MAPS), that displays increased antigenicity, yet lacks excessive innate immunity activation, completely protects gerbils against amoebic
abscess of the liver caused by the intraportal injection of virulent E. histolytica.
Liver abscesses caused by Listeria monocytogenes were not prevented. Invasive E. histolytica may produce the parent
protein of
MLIF in vivo, and if appropriately cleaved, it may play a role in invasive
amoebiasis.
MLIF may join new vaccination strategies against
amoebiasis.