Role of membrane-bound IgM in Trypanosoma cruzi evasion from immune clearance.

We have recently described that Trypanosoma cruzi parasites of the reticulotropic Y strain increase their resistance to antibody-induced clearance during their interaction with the vertebrate host immune system. In the present study, we observed that trypomastigotes of the myotropic CL strain isolated from normal host also display an increased resistance to immune clearance when compared to parasites obtained from immunosuppressed donors. Through fluorescence-activated cell sorting analysis, we have observed that the high expression of membrane-bound IgM antibodies on Y and CL trypomastigotes correlates with their enhanced resistance to Ig-induced clearance. Trypomastigotes from normal mice were essentially refractory to the in vitro binding of immunoglobulins, showing that their membrane structures were completely covered by IgM antibodies. These findings suggest that this isotype does not efficiently mediate immune clearance. Moreover, membrane-bound IgM antibodies limited the amount of IgG attached to the parasite and, as a consequence, impaired efficient immune clearance. Through this mechanism, trypomastigotes of T. cruzi could increase their persistence in the bloodstream thus favoring parasite transmission to its hematophagous host vector in the early acute phase of the disease.

Ig-isotype patterns of primary and secondary B cell responses to Plasmodium chabaudi chabaudi correlate with IFN-gamma and IL-4 cytokine production with CD45RB expression by CD4+ spleen cells.

In this work, the authors analysed T and B lymphocyte subsets and cytokine production in the spleen of BALB/c mice during polyclonal lymphocyte activation (primary infection) and parasite-specific response to Plasmodium chabaudi chabaudi (secondary infection). The secondary response was evaluated in fully immunoprotected animals, 60 days after a chloroquine-cured infection. The authors observed that in polyclonal lymphocyte activation antibody-secreting cells of all isotypes increased, with predominance of IgG2a and IgG3 classes. At that time, IFN-gamma was largely produced, but IL-4/IL-5 were just slightly enhanced. In mice re-infected after 60 days, the Ig-isotype pattern was restricted to IgG1 and only IL-4/IL-5 were produced. In both responses, however, the levels of IL-2 were greatly reduced, while those of IL-10 were enhanced to similar levels. The different involvement of Th1 and Th2 cells in both responses was confirmed through analysis of CD45RB expression by CD4+ cells. The authors observed that CD45RBhigh cells were the major CD4+ subpopulation in primary infected mice, while CD45RBlow cells predominated in 60 days re-infected animals. Moreover, the great majority of activated (large) CD4+ cells in the primary infection belonged to the CD45RBhigh subset, while after reinfection most of the CD4+ large had a CD45RBlow phenotype.

Purification of F(ab')2 anti-snake venom by caprylic acid: a fast method for obtaining IgG fragments with high neutralization activity, purity and yield.

Pooled horse plasma containing antibodies against Crotalus durissus terrificus whole venom were digested with pepsin at an enzyme-substrate ratio of 8:1, pH 3.1, for 40 min and the F(ab')2M fragments purified by adding 8.7% caprylic acid (pH 5.0). For comparison, F(ab')2B purified by precipitation with ammonium sulphate and uncleaved IgG purified with caprylic acid were also prepared. Fab' fragments were obtained by reduction and alkylation of F(ab')2B. The anti-whole C.d. terrificus venom titers, determined by Dot-Blot were 12,800 (IgG), 6400 [F(ab')2B], 4800 [F(ab')2M] and 3200 (Fab'B). Immunochemical analysis of these fragments by SDS gel electrophoresis, Western blot and by double immunodiffusion revealed that the solution containing F(ab')2M was free of IgG and of other plasma proteins, whereas that containing F(ab')2B was not. One milligram of either F(ab')2B, F(ab')2M or Fab'B was able to neutralize respectively 20.7 micrograms, 20.2 micrograms and 13.8 micrograms of C.d. terrificus venom.