The supernatant fluid of axenically grown E. histolytica inhibits chemotaxis, chemokinesis and random mobility of human mononuclear phagocytes (MP) as measured in Boyden chambers. Human polymorphonuclear phagocytes (PMN) locomotion is apparently unaffected. The factor was found in comparable amounts in the supernatant fluid of axenic cultures of four E. histolytica strains that differed in their human pathogenicity and virulence, as well as in two entamoebas non-pathogenic for man. This dialysable and thermolabile MP-locomotion inhibiting entamoeba product (EP) can be absorbed out by incubation with MP, but not with lymphocytes, while partial absorption was observed using PMN. The MP-locomotion inhibitory effect of this EP was cancelled by inhibiting protein synthesis in the MP by means of cycloheximide. In vivo, this EP caused a delay in MP migration in Rebuck skin windows. The molecular weight of this EP lies between 478 and 765 by gel-sieve chromatography. Our results suggest a direct effect upon the cytoskeletal and locomotive apparatus of the MP. This MP-locomotion inhibiting EP could contribute to the paucity of the inflammatory reaction observed in the advanced stages of invasive amoebiasis and consequently also to the lack of scar tissue formation upon healing of amoebic lesions.

The bactericidal capacity of mononuclear and polymorphonuclear phagocytes obtained from normal newborn infants and from healthy adults was evaluated in vitro, using two group B beta-hemolytic streptococci (GBBHS) serotypes (GBBHS-Ia-SS-615/28 and GBBHS-III-SS-620/50) and uniform opsonic conditions. No intertype differences in bacteriolysis of these two serotypes were observed among leukocytes from newborns or adults. As group, only polymorphonuclear phagocytes from newborns disclosed a significantly lower mean bactericidal capacity than their adult cellular counterpart, and only with respect to GBBHS-III-SS-620/50. On the other hand, 4 or 16 polymorphonuclear samples from newborns tested revealed significantly low bactericidal capacities against both GBBHS serotypes, and an additional sample revealed a bactericidal capacity against GBBHS-III-SS-620/50 alone. Interstrain variations in the intrinsic bactericidal capacity of polymorphonuclear phagocytes from newborns against GBBHS-III may exist, as suggested by a single observation made by using four clinical isolates of GBBHS-III. Such deviant phagocytic capacities of polymorphonuclear phagocytes from newborns may constitute an additional selective risk factor in the genesis of GBBHS sepsis of the newborn.

SummaryUnder-agarose random migration, chemokinesis and chemotaxis of monocytes from 36 patients with Down's syndrome were compared to those of monocytes from 42 healthy, age-matched control children. Random migration of monocytes from patients with Down's syndrome was comparable to that of controls. In contrast, chemotaxis of monocytes from patients with Down's syndrome was significantly decreased (P < 0.001) when com~ared to that of controis, even though chemokinesis was significantly increased (P < 0.001). Age, sex, and physical development of patients with Down's syndrome or of control children included in this study had no apparent effect upon monocyte mobility. Abbreviations CS, control serum DS, Down's syndrome MP, mononuclear phagocytes ZAS, zymosan-activated serum Increased susceptibility to infection in patients with DS (22,28) may reflect several abnormalities in host defense mechanisms involving humoral and cellular immune responses (2, 17) and the inflammatory-phagocytic process (13,15,27). No defect can be singled out as the most important one, hence the definition of the immunodeficiency of DS as a complex sum of several immunologic faults of variable intensity that can change with age (4). Cellmediated immunity in DS is predominantly impaired at its effector site (34): depressed in vitro lymphocyte responses, anergy or weak delayed type hypersensitivity skin reactions and decrease in circulating T cells have been reported in patients with DS (16,17), although lymphocytosis with high counts of T and B cells may be found in older, institutionalized patients (34).MP and lymphocytes constitute the bulk of the inflammatory cells in delayed hypersensitivity reactions, MP playing a crucial role in phagocytosis as well (5). Accumulation of mononuclear cells at such inflammatory sites depends largely on their response to chemotactic signals. Poor mobilization of these cells may contribute to the weakness of delayed hypersensitivity and other inflammatory reactions in DS (6). We measured random migration, chemokinesis (enhancement of random migration) and chemotaxis (directional migration) of MP from patients with DS and compared them to those of healthy age-matched children. We employed the agarose-plate method (21), which is less expensive, simpler, and more reproducible than the Boyden chamber method, even though the relative sensitivity of the two assays is still somewhat controversial (14,19). Only MP of a mononuclear leukocytes population seem to contribute to the migration pattern using the agarose device (21). MATERIALS AND METHODSPatients and controls. Thirty-six home-cared patients with DS (Trisomy 21: 14 females, 22 males, 6 months to 7 years of age) were studied. None of the patients had leukemia, suffered of overt infection or took any medication within 2 wk of the study. Fortytwo healthy children (15 females, 27 males, 6 months to 7 years of age) undergoing elective orthopaedic surgery, and matched as closely as possible with the patients for similar age and sex were used as controls. Differe...

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Unlike normal (i.e., non-activated) human eosinophils that are unable to destroy virulent Entamoeba histolytica even in the presence of antibodies and complement, activated eosinophils effectively destroy the parasite in vitro without the help of opsonins, yet increase this capacity with their assistance. Many activated eosinophils succumb in the process as well, probably victims of toxic products released by dying amoebae. Human activated eosinophils thus behave more like activated macrophages than like neutrophil polymorphonuclear leucocytes that are notoriously incompetent in dealing with virulent amoebae. As a regular constituent of early inflammatory reactions, and notwithstanding the absence of blood and tissue eosinophilia in invasive amoebiasis, the activated eosinophil may play a role in the defence against E. histolytica.

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.

Amebiasis is a major health problem in developing countries. Entamoeba histolytica infects 5 x 10 8 people worldwide, more than 90% of them living in West and South East Africa, China, SE Asia, México, the western portion of South America and India (Smyth 1994). Only 10% of all infected individuals eventually develop invasive amebiasis ranging from mild (i.e. self-limited) or serious intestinal amebiasis, to life-threatening hepatic invasion (Walsh 1986).It has been suggested that there are in fact two different species of Entamoeba. One, the classic pathogenic E. histolytica discovered by Schaudinn in 1903. The other, the non-pathogenic E. dispar described by Brumpt in 1925, based mainly on epidemiological considerations. The concept of two Entamoeba species began to be objectively established by functional in vitro studies (Martínez-Palomo 1982, Mirelman & Chayen 1990) and zymodeme patterns (Sargeaunt 1988), culminating now with molecular genetic data (Tannich & Burchard 1991, Tannich 1996.Thus, the majority of ameba infected individuals may actually harbour E. dispar, leaving the E. histolytica as the agent of the relatively rare invasive intestinal and extraintestinal disease. Amebic abscess of the liver (AAL) on the other hand, occurs in less than 1% of individuals with invasive intestinal amebiasis (Martínez-Palomo et al. 1993).Why the vast majority of individuals (≥99%) appear to be resistant to extraintestinal invasion remains unknown but some inroads have now been made: a significant increase in the SCO1 complotype and in HLA-DR3 was found in 160 Mexican mestizos (adults and children) with AAL when compared to healthy controls, to adult patients with amebic rectocolitis or to asymptomatic amebic carriers (Arellano et al. 1996). DNA subtyping is now in process to confirm these findings.Studies of human amebiasis and of experimental animal models of amebic disease have suggested that cell-mediated rather than humoral immune mechanisms, are responsible for acquired immunity to AAL (De León 1970, Salata & Radvin 1986, Kretschmer & López-Osuna 1990. Moreover, axenically grown trophozoites of E. histolytica kill in vitro normal human neutrophils and eosinophils (not-withstanding the aid by antibody and complement), normal monocytes and lymphocytes, without suffering changes in their own viability (Jarumilinta & Kradolfer 1964, Artigas et al. 1966, Guerrant et al. 1981, Salata et al. 1985, 1987, López-Osuna et al. 1986, López-Osuna & Kretschmer 1989 fectively destroying virulent amebas, even though finally succumbing in the process as well (Salata et al. 1985). In our laboratory we found that the same occurs with activated human peripheral blood eosinophils (López-Osuna et al. 1992).There is no circulating eosinophilia in most protozoan infections, yet this is not necessarily an argument against their possible participation in AAL, specially because eosinophils are regularly found in the early inflammatory stages of experimental amebic liver disease (Tsutsumi et al. 1984), and since the bulk of eosinophils in ...

We evaluated the in-vitro interaction of normal human eosinophil leucocytes and a virulent strain of Entamoeba histolytica (HM1-IMSS) in the presence of immune serum. At a 10:1 (eosinophil:amoeba) ratio a significant time-dependent destruction of eosinophils was found from the first hour onward, and a similar, albeit weaker, cytopathic effect was found in the 200:1 ratio mixtures, with some delay in the microscopic evidence of such effect. Results were unaffected by serum factors, and amoebae emerged virtually unharmed throughout these experiments, again regardless of the presence of serum factors. These results indicate that, as with neutrophil leucocytes, virulent E. histolytica is capable of destroying normal human eosinophils in vitro.