Loss of the GP46/M-2 surface membrane glycoprotein gene family in the Leishmania braziliensis complex.

Immunization with the GP46/M-2 membrane glycoprotein of Leishmania amazonensis has been shown to induce a protective immune response against infection. We have surveyed a variety of trypanosomatid species and genera for the presence and expression of this gene family, information that will be relevant to future vaccine studies against leishmaniasis. Molecular karyotype analysis revealed the presence of GP46/M-2 genes in all members of the Leishmania mexicana complex, Leishmania major, Leishmania donovani, Leishmania tarentolae, and Crithidia fasciculata. In contrast, DNAs from species of the Leishmania braziliensis complex (L. braziliensis, Leishmania guyanensis, and Leishmania panamensis) failed to hybridize to GP46/M-2 probes. Western blot analyses with several polyclonal antisera against the GP46/M-2 protein revealed protein expression in L. major and L. donovani, but not L. panamensis or L. braziliensis. Phylogenetic analysis suggests that a loss of the GP46A gene family occurred following separation of the L. braziliensis complex, prior to speciation events within this complex. These data indicate that GP46/M-2 membrane glycoprotein may not be critical to parasite survival, but may play an ancillary role during the developmental cycle.

Decreased low-density lipoprotein receptor function and mRNA levels in lymphocytes from uremic patients.

The mechanisms by which renal failure causes hyperlipoproteinemia remain unclear. To investigate the potential role of the low-density lipoprotein (LDL) receptor in lipoprotein metabolism in uremia we measured LDL receptor function in peripheral blood mononuclear cells (PBMC) from uremic patients and control subjects using a functional assay in which proliferation of lectin-stimulated PBMC in the presence of lovastatin was dependent upon internalization of exogenous cholesterol via a functional LDL receptor. The amount of LDL required to reverse 50% of lovastatin-induced inhibition of proliferation in PBMC from uremic patients was significantly greater (3.6 +/- 1.8 micrograms/ml, N = 33, P < 0.05) than controls, (1.99 +/- 0.6 micrograms/ml, N = 37). Abnormal LDL receptor function in four uremic patients normalized following renal transplantation. To investigate the molecular basis for LDL receptor dysfunction, we directly quantitated LDL receptor messenger RNA (mRNA) in PBMC from uremic patients and control subjects using a ribonuclease protection assay. LDL receptor mRNA expression in uremic patients was 0.42 +/- 0.08 (N = 10), significantly lower (P < 0.015) than in normal subjects, 0.71 +/- 0.08 (N = 14). These data suggest that an acquired defect in LDL receptor function in PBMC from uremic patients exists which may be due to decreased LDL receptor expression. These abnormalities, if present in other tissues, could contribute to the aberrant lipoprotein metabolism which is a consistent feature of uremia.