Rate-zonal centrifugation of herpes simplex virus-antibody complexes

Rate zonal centrifugation can partially separate platelets from platelet-derived vesicles

BACKGROUND

Centrifugation is commonly used as a first step to enrich biomarkers from blood. Biomarkers are separated on the basis of density and/or diameter. However, the centrifugation protocol affects the yield and purity of biomarkers, for example, isolation of platelets results in co-isolation with extracellular vesicles (EVs).

OBJECTIVE

To assess the ability of rate zonal centrifugation (RZC) to separate platelets from co-isolated EVs.

METHODS

Using a linear Optiprep gradient, RZC was able to separate a mixture of beads with different diameters but similar density. Next, RZC was applied to samples containing both platelets and platelet-derived EVs (n = 3). After RZC, all fractions were collected and stained with anti-CD61-Alexa 488 to measure the concentrations of platelets and platelet-derived EVs by flow cytometry.

RESULTS

We confirm that RZC separates polystyrene beads with diameters of 140 nm, 380 nm and 1,000 nm. Next, we show that the majority of platelets occur in fractions 8-19, whereas the majority of platelet-derived EVs are detectable in fractions 1-7. Furthermore, each fraction contains a different diameter range of platelets, which suggests that separation is indeed diameter based.

CONCLUSION

RZC can partially separate platelets from EVs.

Complement, viruses, and virus-infected cells

The attachment of specific antibody to viral glycoproteins and other structures on the surface of a virus or virus-infected cell has a number of potential consequences to the virus or virus-infected cell. Antibody is multivalent and thus able to redistribute or patch surface viral proteins or virus-encoded structures within the lipid bilayer of the viral envelope or the cell membrane. In certain instances, antibody may agglutinate viruses or virus-infected cells. The physical presence of antibody molecules on the virus surface may interfere with the ability of the virus to infect potentially susceptible cells. Antibody on the surface of virus-infected cells may prevent the maturation and release of virus particles; antibody also can alter certain normal cell functions. The Fc portions of antibody molecules bound to virus-infected cells facilitate interactions with effector cells bearing Fc receptors. In the case of lymphocytes and perhaps phagocytic cells, this interaction may lead to antibody-dependent cellular cytotoxicity (ADCC) [51, 58]. The exposed Fc regions may also facilitate attempts at ingestion by monocytes, macrophages, and polymorphonuclear leukocytes.

Neutralization of Epstein-Barr virus by nonimmune human serum. Role of cross-reacting antibody to herpes simplex virus and complement

These studies were carried out to investigate the mechanism of neutralization of purified Epstein-Barr virus (EBV) by fresh human serum from normal individuals lacking antibody to the EBV viral capsid (VCA) and nuclear antigens (EBNA). Such individuals thus lack serological evidence of immunity to EBV. Although an enzyme-linked immunosorbent assay (ELISA) with highly purified immobilized EBV detected low levels of IgG antibody reactive with EBV in these normal nonimmune sera, this antibody failed to neutralize EBV in the absence of complement. Studies with depleted sera and mixtures of purified complement proteins at physiologic concentrations showed that the IgG antibody and C1, C4, C2, and C3 of the classical pathway were able to fully neutralize EBV. Mixtures of the purified components of the alternative pathway at physiologic concentrations failed to neutralize purified EBV in the presence or absence of the antibody and the alternative pathway did not potentiate classical pathway-mediated neutralization. No evidence for a requirement for C8 was obtained, precluding lysis as the mechanism of neutralization. Since C3 deposition on the viral surface accompanied classical pathway activation, viral neutralization is most likely secondary to the accumulation of complement protein on the viral surface. A coating of protein on the virus could interfere with attachment to, or penetration of potentially susceptible cells. Experiments were undertaken to determine the specificity of the IgG antibody in the sera of EBV nonimmune individuals which, together with complement, neutralized EBV. Both purified EBV and herpes simplex I (HSV-1) absorbed the EBV ELISA reactivity and EBV-neutralizing activity of nonimmune sera, whereas another member of the herpesvirus group, cytomegalovirus, was inactive in this regard. HSV-1 was quantitatively more efficient than EBV in absorbing reactivity, a finding that indicates that the antibody has a higher affinity for HSV-1 than for EBV. Further absorption studies indicated that the cross-reaction occurred in both directions as EBV also absorbed HSV-1 reactive antibodies as tested in an HSV-1 ELISA. EBV was also less efficient than HSV-1 in absorbing reactivity with HSV-1. A serum lacking detectable antibodies to both EBV and HSV-1 failed to neutralize EBV. These studies cumulatively indicate that fresh serum from EBV nonimmune individuals neutralizes EBV by the combined action of a previously undescribed cross-reacting antibody apparently elicited by HSV-1 and C1, C4, C2, and C3 of the classical complement pathway.

Analysis of poliovirus antibody complexes by density gradient centrifugation

Analysis of poliovirus antibody complexes by sucrose density gradient centrifugation demonstrated differences in behavior of sensitized virus between early and late serum, particularly with regard to neutralizing capacity of different concentrations of antiserum.

Neutralization of animal viruses

Various aspects of the interaction of bacterial viruses and antibody were studied by Andrewes and Elford in England. Similar studies, as well as studies on animal viruses, were carried out in Australia by Burnet and his colleagues. One result of their extensive studies, which were summarized in great detail, was the conclusion that, with respect to their interaction with antibody, bacterial and animal viruses were basically different. Specifically, the difference resided in the stability of the union of virus and antibody, whereas bacterial viruses formed stable complexes, animal viruses formed complexes that tended to dissociate readily. The introduction of animal cell cultures as host systems greatly aided in the study of animal viruses, with respect to fewer and more readily controlled variables, and by the use of the plaque assay in enhanced quantitative reliability. In 1956, Dulbecco et al. described the interaction of two animal viruses with their respective antibodies. The results of these studies led these investigators to conclude, among other things, that animal viruses, at least the two they studied, reacted with antibodies to form complexes that did not dissociate spontaneously. This interpretation was challenged by Fazekas de St. Groth and Reid. As more animal virus-antibody systems were studied by many investigators, there seemed to be a greater accord for irreversible, rather than reversible, interaction. For this reason, in this chapter it is assumed that there are no differences between bacterial viruses, as one category, and animal viruses, as a separate category, concerning their interaction with antibodies. Rather, differences, when they exist, are considered to be related to the viruses per se. Although this chapter is intended to survey the neutralization of animal viruses, occasional reference is made to the studies on bacterial viruses when these studies are pertinent and illuminating to the topic at hand.

Formation and biologic role of polyoma virus-antibody complexes. A critical role for complement

Interaction of polyoma virus, specific antibody, and complement has been studied. Firm evidence has been gathered that C1 through C3 and not C5 through C9 enhance neutralization of virus-antiviral antibody (V-Ab) complexes. C enhancement of neutralization occurs primarily by agglutination of V-Ab complexes and not by virion lysis or attachment of large protein molecules to the V-Ab complex. In this model, binding of C1, 4, 2, 3 to the V-Ab complex may explain why some viruses concentrate in or infect certain cells bearing C3 receptors such as B lymphocytes, macrophages, and monocytes.

Incorporation of labeled precursors into the RNA and proteins of lactic dehydrogenase virus

Lactic dehydrogenase virus was grown in primary mouse embryo cells and labeled with (3)H-uridine and (3)H-amino acids. Concentrated and purified virus was banded by isopycnic centrifugation in sucrose gradients, and infectivity and radioactivity were found to correspond at a density of 1.17 g/cm(3). The extracted viral RNA was resolved by electrophoresis in polyacrylamide-agarose mixed gels, and the mol wt was estimated to be 6.0 x 10(6).

Comparison of direct and indirect solid-phase microradioimmunoassays for the detection of viral antigens and antiviral antibody

Viral antigens were fixed to the surface of microtiter wells, and serial dilutions of antiviral antibody were added. The amount of antiviral antibody bound to viral antigens was determined by measuring the extent to which the antiviral antibody either inhibited the specific binding of (125)I-labeled antiviral immunoglobulin G (IgG) (direct technique) or enhanced the specific binding of (125)I-labeled anti-IgG (indirect technique). Immune complexes composed of viral antigens and antiviral antibody (human) could be detected by the binding of (125)I-labeled rheumatoid factor. Specific binding was influenced by the concentration of protein in the diluents used during the different steps of the procedure. A high concentration of protein in the diluent used with the viral antigens decreased specific binding, whereas a high concentration of protein in the diluent used with (125)I-labeled anti-IgG increased specific binding by decreasing nonspecific attachment of the labeled anti-IgG. Under the conditions employed, the titer of a given antiviral serum was several hundredfold greater by the indirect than by the direct technique.