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The role of electrostatic interactions in the attachment and fusion at acidic pH of Sindbis virus (SNV) with goose erythrocytes was studied, investigating the effect of several anionic and cationic polyelectrolytes on SNV hemagglutination and hemolysis. In order to establish the target of active drugs, the compounds were incubated either with the virus particles or with the erythrocytes. Dextran sulfate was the only compound able to inhibit the attachment of SNV to the erythrocytes. Fusion of virus with red cells was reduced dose-dependently by the polyanions dextran sulfate, mucin and polygalacturonic acid. On the contrary two polycations, polylysine and polybrene, enhanced viral hemolytic activity. However the effect of polyions is not exclusively related to the electric charge since ineffective molecules were found in both classes of compounds.

In the present work the non-antibody inhibitory activity of human serum towards SA-11 rotavirus hemagglutination (HA) has been studied. Among human serum protein components, inhibitory activity was recovered in fractions III (beta-globulin), IV (alpha-globulin) and IV (glycoprotein). Additional experiments performed with purified lipoprotein sub-classes and their lipid and apolipoprotein moieties demonstrated the ability of HDL and, HDL1 to prevent SA-11 HA.

Results are reported concerning the extraction and purification of gangliosides present in CER cells, a cell line which is highly suitable for the cultivation in vitro of rabies virus. By means of thin layer chromatography it has been possible to demonstrate that the CER cell ganglioside pattern is composed mainly of monosialo and disialogangliosides.

The adhesiveness of a mucous strain of Pseudomonas aeruginosa to rabbit bladder mucosa was studied after preincubation of the microorganism with several glycolipids with different carbohydrate moieties to investigate their importance in the interaction with bacterial adhesins. Vesical cells were also treated with lectins (limulin and soybean) to confirm the role of saccharides as membrane receptor. The results obtained showed that galactose-containing glycolipids were able, in varying degrees, to reduce bacterial binding. The most active compounds were glycosphingolipids with negatively charged terminal groups. Lectin treatment of bladder mucosal cells confirmed the importance of galactose and sialic acid as mucosal cell membrane receptors for P. aeruginosa.

In order to elucidate the mechanisms involved in the antibacterial activity of lactoferrin, quantitative determinations of siderophore production and lactoferrin adsorption on various bacterial species were performed. The binding of lactoferrin took place both on Gram-positive and Gram-negative species and occurred with bacterial cells grown in stress or in excess of iron. The different degrees of sensitivity to lactoferrin observed could not be directly related to the type and amount of siderophores produced. However, it was possible to find a correlation between the capacity of some strains to bind lactoferrin and their sensitivity to this protein. These data suggest that the binding of lactoferrin on the cell surface can result in an antibacterial activity additional to iron witholding.

Early interactions between vesicular stomatitis virus (VSV) and susceptible cells were examined in cell lines of mammalian (HeLa), bird (CER), piscine (EPC) and arthropod (Aedes albopictus) origin showing different permissiveness to VSV growth. The chemical nature of receptors was investigated either by modification of cell surfaces with different enzymes or by competition for VSV binding between extracted membrane components and whole cells. Results obtained indicate that in all cell models, membrane lipid components show receptor activity whereas glycid groups participate to the in virus binding to a different extent.

The chemical nature of Sindbis virus receptors on goose erythrocytes was investigated by means of two different experimental approaches: by testing the capacity of human serum lipoproteins (HDL, LDL, VLDL) to compete with erythrocytes for virus binding and by enzymatic and chemical modifications of the cell membrane. Each class of lipoproteins was separated into its protein and lipid components which were tested for hemagglutination and hemolysis inhibiting activity. Only the lipid moieties were able to inhibit binding and fusion activities of the virus. Enzymatic treatments of the erythrocyte surface showed that sialic acid and trypsin-sensitive proteins were not involved in Sindbis virus membrane receptor and that some phospholipids probably represent important components of the cellular binding site.

The inhibiting activity of various human serum lipoprotein classes and their lipid components on the infectivity of rhabdoviruses has been studied. The research has been carried out according to different experimental procedures on both the vesicular stomatitis virus (Indiana strain), and the fixed rabies virus (CVS strain). The results obtained have shown an inhibition of the infectivity of VSV and CVS, mainly linked to the very low and low density lipoprotein classes. It has also been demonstrated that the inhibitors act directly on viruses causing a decrease in their attachment to host cells.

In the present report an attempt was made to elucidate the role of gangliosides in early interactions between vesicular stomatitis virus (VSV) and CER cells. Research was carried out to test the ability of gangliosides from mammal brains and from CER cells to inhibit viral attachment to susceptible cells. The incubation of VSV in the presence of gangliosides decreased the subsequent infection of CER cells by the virus. When similar experiments were performed with gangliosides inserted in liposomes the inhibition of infection was enhanced. Since carbohydrate moieties could participate to rhabdovirus binding as a part of a glycolipid receptor, CER cells were subjected to the action of glycosidases and these produced a fall in the viral attachment. Deglycosilated CER cells reacquired their susceptibility to virus infection after coating with gangliosides immediately after enzyme treatment. Results obtained show the participation of gangliosides in the receptorial structure for vesiculovirus of susceptible CER cells.

Neuraminidase production by reference strains of various group B streptococci serotypes was investigated before and after serial passages in mouse. The enzyme production was tested in culture filtrates using bovine submaxillary mucin as substrate. Although passages in mouse markedly increased the virulence of all the strains it was not possible to demonstrate a relationship between the increased virulence and the enzyme production.

The involvement of lipid components in hepatitis A virus (HAV) attachment to host cells has been investigated. Isolated Frp/3 cell membranes and whole lipids, phospholipid and glycolipid fractions extracted from them were able to bind the virus and to prevent infection. Treatment of virus with various phospholipids or glycolipids demonstrated the participation of phosphatidylserine, phosphatidylethanolamine and galactose in HAV binding. Results obtained added further information on the receptor specificity of host cells for HAV.

The role of mannose containing molecules in Sindbis virus envelope glycoproteins and cell membrane receptors was investigated by means of concanavalin A (con A). Treatment of virus or BHK 21 cells with the lectin before infection reduced viral infectivity. Hemagglutination and hemolysis showed a different sensitivity to con A. Hemagglutination was not affected by the lectin and treatment of erythrocytes with con A produced an enhancement of agglutinability by the virus. Hemolytic activity was, on the contrary, strongly reduced by the lectin. The inhibition observed is due to an action on viral structures and not to an interaction with erythrocyte receptors because con A did not affect the hemolysis when preincubated with erythrocytes.