Merozoites are the invasive stage of the malaria parasite, which are released from infected erythrocytes to invade other erythrocytes. Antibody to surface antigens on merozoites may prevent invasion by agglutinating merozoites as they are released from infected erythrocytes or by blocking receptors before contact of merozoites with the host erythrocyte. Monoclonal antibodies were produced to a 140,000-m.w. protein on the merozoite surface. The protein was synthesized by the mature intraerythrocytic parasite, the schizont, as a 143,000-m.w. protein and had a m.w. of 140,000 on the surface of free merozoites. The monoclonal antibodies were shown to bind to the surface of merozoites by immune electron microscopy. Ascitic fluid containing four of 11 anti-140,000 monoclonal antibodies partially blocked invasion of erythrocytes by merozoites released from schizont-infected cells. The low invasion rate was always associated with a high frequency of multiply infected erythrocytes (two or more rings per erythrocyte). Monoclonal antibodies purified by (NH4)2SO4 precipitation and diethylaminoethyl column fractionation also blocked invasion and caused multiple invasion of individual erythrocytes. The monoclonal antibodies, incubated with free merozoites, did not block invasion, indicating that the antibodies did not bind to merozoite receptors for erythrocytes. We propose that the reduced rate of invasion and the multiple invasion of erythrocytes, the characteristic of these monoclonal antibodies, was caused by weak agglutination of merozoites as they were released from infected erythrocytes.
Protective or therapeutic immunity against HIV infection is currently believed to require both antibody and CTL responses against the envelope protein. In the present study, the adjuvant activity of a unique oil‐in‐water emulsion, in which liposomes containing lipid A (LA) and encapsulated antigen served as the emulsifying agent, was examined in mice using oligomeric gp140 (ogp140) derived from the HIV‐1 envelope as the antigen. Emulsions rendered either highly stable or unstable by altering the ratio of liposomes to oil were used to examine the effect of stability of the emulsion on adjuvant activity. Stable and unstable emulsions had similar potencies for inducing both IgG antibodies to ogp140 and antigen‐specific T‐lymphocyte proliferation. Stable emulsions, but not unstable emulsions, induced antigen‐specific CTL responses, possibly because of the depot effect of the stable emulsions. Furthermore, stable emulsions induced lower IgG2a/IgG1 ratios than the unstable emulsions. We conclude that stable liposomal oil‐in‐water emulsions provide an effective means of obtaining both antibody and CTL responses against an HIV envelope antigen.
Our goal is a liposomal delivery system of membrane-linked botulinum toxin type B heavy chain (BoNT/B HC) to specifically target therapeutics to neuronal cells. Unilamellar liposomes (~200 nm) containing egg phosphatidylcholine, sphingomyelin, cholesterol, and cholest-5-en-3β [dithiopyridine] (to couple HC SH group to liposomes) were prepared by extrusion. Coupling of BoNT HC to the liposomal surface was verified by flow cytometry (FC) using liposomes containing Rhodamine-labeled phospholipid (N-Rh-PE) and FITC-labeled HC. FC was used to determine binding specificity of liposomes with or without coupled BoNT-HC to SH-SY5Y (neuronal cells) or PC12 cells (control cells lacking BoNT/B receptors). N-Rh-PE-liposomes with or without coupled FITC-HC were incubated with cells and cell-associated fluorescence determined. Liposomes alone did not bind to either cell line until >45 min of incubation. Free HC or liposomes coupled to BoNT HC bound to the SH-SY5Y cells, but not to control PC-12 cells except when the cells loaded with the BoNT/B ganglioside receptor GT1b. Since liposomes can deliver encapsulated drugs to cells, our BoNT/B HC-coupled liposomes form the basis for delivery of BoNT therapeutics to intoxicated neuronal cells. The opinions or assertions are the private views of the authors, and not official views of the Department of the Army or the Department of Defense. Supported by DTRA 3.10032_08_WR_B.
Seventeen malaria-naive volunteers received a recombinant Plasmodium falciparum vaccine (RLF) containing the carboxy- and the amino-terminal of the circumsporozoite protein (CSP) antigen without the central tetrapeptide repeats. The vaccine was formulated in liposomes with either a low or high dose of 3-deacylated monophosphoryl lipid A (MPL) and administered with alum by intramuscular injection. Both formulations were well tolerated and immunogenic. MPL increased sporozoite antibody titers measured by ELISA, Western blot, and immunofluorescence assay. One high-dose MPL vaccine formulation recipient developed a CSP-specific cytotoxic T lymphocyte response. After homologous sporozoite challenge, immunized volunteers developed patent malaria. There was no correlation between prepatent period and antibody titers to the amino- or carboxy-terminal. The absence of delay in patency argues against inclusion of the amino-terminal in future vaccines. A significant cytotoxic T lymphocyte response may have been suppressed by the inclusion of alum as an adjuvant.
Naturally-occurring antibodies against simple glycolipids have been described only in scattered reports in the literature. About 75% of all normal humans have complement-activating anti-Forssman activity (1), and a monoclonal Waldenstrom macroglobulin IgM antibody (McG) having specificity for Forssman glycolipid was derived from the plasma of a patient (2,3). Some normal, or abnormal, human sera have anti-monogalactosyl (4) or anti-digalactosyl diglyceride antibodies (5). Recently we reported the occurrence of "natural" antibodies, apparently autoantibodies, with specificity against di- and trihexosyl ceramide haptens (CDH and CTH), in normal rabbit sera (6). We also found natural anti-ganglioside GM1 antibodies in normal human, guinea pig, and rabbit sera (7). The major purpose of the present study was to describe, and to quantify, the widespread occurrence of natural complement-fixing autoantibodies against numerous simple glycolipids. We show that every individual rabbit and human serum tested had complement-fixing autoantibodies against glycolipids that are widely distributed in circulating blood
