Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographies: leaves 30-31, 83-85.

The antibody response has evolved under constant pressure to recognize common pathogens and also remain adaptable to novel threats. Given the limited size of the germline antibody repertoire, adaptability requires that some antibodies must be polyspecific for multiple distinct antigens. Despite the profound importance of polyspecificity in the antibody response, the structural features that allow it are not well understood. Antibodies raised against glycoconjugates of Chlamydiaceae LPS oligosaccharides of the inner-core sugar Kdo (3-deoxy-d-manno-oct-2-ulosonic acid) have been shown to cross-react with several inner-core oligosaccharides through conserved recognition of single Kdo residues in a germline-encoded pocket, with additional sugars accommodated by flexible side-chains. Two of these antibodies, S25-2 and S25-39, were observed to bind several Kdo oligosaccharides with an identical binding site conformation, but adopted unique conformations of the heavy chain complementarity determining region loop 3 (CDR H3) in the absence of ligand. Conformational flexibility of germline antibodies is believed to facilitate polyspecificity by generating multiple unique binding sites in a single antibody. This thesis research further explores the conformational flexibility of the antibodies S25-2 and S25-39 to gain insight into mechanisms of antigen recognition and how this feature may allow polyspecificity. This was achieved first by solving structures of S25-39 from crystals grown in unique conditions to observe alternate CDR H3 conformations, and second by designing synthetic Kdo-based antigens so as both to inhibit interaction with the previously observed liganded conformation of S25-2 and S25-39 and to be accommodated by their observed unliganded conformations. These structures reveal an unprecedented level of structural diversity of CDR H3, notably including the exact ‘liganded’ conformation in the absence of ligand. This is the first direct structural evidence that CDR H3 can exist in a conformational equilibrium with antigen binding through a selection mechanism, as opposed to induced fit where antigen causes the observed conformational change. Definitive evidence for binding the synthetic antigens was not obtained, however the resulting structures revealed several additional unique conformations of CDR H3 suggesting that ligands can alter conformational equilibria during crystallization. A unique conformation was also observed with CDR H3 coordinating multiple iodide ions, revealing another potential source of polyspecificity with unique binding paratopes generated by ion coordination. Finally, the unparalleled level of conformational diversity observed for these antibodies highlights the challenges of antibody structure classification and prediction, and stresses the need for additional in-depth studies of conformational diversity and binding mechanisms to advance these fields for therapeutic application. This is the first targeted structural study of flexibility in antibodies and provides insight into their conformational dynamics and antigen-binding mechanisms. These are of fundamental importance in understanding antibody structure and function, a critical consideration in practical applications such as modelling and design of therapeutic or diagnostic antibodies. / Graduate / 2019-11-27

Several cellular and subcellular fractions were prepared from Pseudomonas aeruginosa strain PA-7. Those found to be immunogenic in rabbits included a heat-stable lipopolysaccharide, a protein-lipopolysaccharide complex, a cell wall preparation arid a formalin-killed whole cell vaccine. However, a lipopolysaccharide preparation extracted with phenol and water was found to be a poor immunogen in rabbits. The cell wall fraction proved to be the most effective immunogen in terms of the amount of antibody evoked, and of the duration of the serum antibody response. Hyperimmune sera produced against all four antigens were found to contain a mixed population of 2-mercaptoethanol sensitive and 2-mercaptdethanol resistant antibodies. Gel filtration and ion exchange chromatography studies established the presence of both IgM and IgG immunoglobulins in all four types of hyperimmune serum. Whole immune serum, as well as the IgM and IgG serum fractions, afforded passive protection to mice challenged with twenty or more LD₅₀ of viable organisms. There was an indication that the IgG fraction of two of the four serum types provided better protection than did the IgM fraction, but precipitation studies indicated that this may have been due to greater numbers of IgG immunoglobulins. In addition serum containing a high proportion of 2-mercaptoethanol resistant antibody-was found to promote faster clearance of injected bacteria than did serum taken earlier in the response. Immunodiffusion studies indicated that all four antigenic preparations contained at least one common immunogen; moreover, all serum types were able to react with sheep red blood cells coated with the heat-stable lipopolysaccharide preparation in passive hemagglutination and hemolysin tests. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

It was established that antibodies could be evoked in rabbits against ferredoxin purified from cultures of Clostridium pasteurianum and against its performic acid oxidized derivative. The extent of cross-reaction was studied between the two antisera and four related antigens: native ferredoxin, iron-sulfide free ferredoxin, performic acid oxidized ferredoxin, arid S-carboxymethylated ferredoxin. All combinations demonstrated cross reactivity by complement fixation, and in the case of oxidized ferredoxin antiserum, three preparations, native ferredoxin, iron sulfide free ferredoxin, and performic acid oxidized ferredoxin precipitated antibody. The data obtained with these cross-reactivity studies Indicated that the cysteine-containing regions of the ferredoxin molecule were not critically involved as antigenic determinants. The C-terminal region of the protein was considered for further study. This octapeptide was synthesized and tested for its ability to combine with antibody directed against both native ferredoxin and its performic acid oxidized derivative. The peptide exhibited specific binding to both antisera as demonstrated by inhibition of complement fixation and precipitation, and by equilibrium dialysis experiments. It is suggested that C. pasteurianum ferredoxin is antigenic in rabbits, that cysteine residues are not involved in at least two of the antigenic regions of the protein, and that the C-terminal octapeptide is one of the antigenic determinants of this molecule. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

The effect of continual antigenic stimulation on the immune system of mice was studied using two different experimental approaches. A GVHR was induced in Fi mice by the injection of parental spleen cells at weekly intervals. Several weeks later the spleen cells of mice undergoing a GVHR were shown to be immunosuppressed as their in vitro responses to the mitogens Con A and LPS were substancially lower than control animals. The serum from these treated mice was also immunosuppressive to normal spleen cells. The proliferative response to Con A and allogeneic cells of normal: syngeneic, allogeneic, and parental spleen cells was 90% suppressed when GVH serum was added in comparison to the addition of normal serum. Similarly, the in vitro antibody response to a T dependant antigen was impaired; however, the antibody response to a T independant antigen was not impaired. These results indicate that T cell functions are more sensitive than are B cell function to immunosuppressive factors in the serum of mice undergoing a GVHR. The serum was fractionated by gel filtration on a Bio-Gel P-200 column. The inhibitory material in GVH serum eluted in the immunoglobulin fraction of serum which indicate that it has a molecular weight of 150,000 or greater. The second approach studied involved continual allogeneic stimulation. Parental type mice were injected at five day intervals with Fi spleen cells in order to induce a HVG reaction. After several injections the spleen cells from these mice were tested in vitro. The spleen cells from HVG mice responded the same as normal spleen cells to the mitogens Con A and LPS. The spleen cells from HVG mice showed an enhanced in vitro antibody response as compared to normal spleen cells. This enhancement was attributed to the allogeneic effect. This series of experiments have shown that the induction of a GVHR in mice can later lead to immunosuppression and production of immunosuppressive factors in the serum of these mice. The induction of a short term HVG reaction has no adverse effects on the immune system except for enhancing an antibody response. It is possible that a more prolonged HVG reaction would parallel the immunosuppression observed in mice undergoing a GVHR. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

Recent work has shown that in vitro, the cytotoxic immune response to cell surface antigens is enhanced if the antigen to which the immune response is directed, is on cells bearing major histocompatibility antigens identical to those of the responding cells. This 'H-2 restriction' has been demonstrated in the mouse using virally infected cells, haptenated cells, cells bearing the male Y antigen, and cells differing at the minor histocompatibility loci. Other investigations have shown that antigenic determinants coupled to tolerated antigens or isologous serum proteins, elicit a humoral response which is weaker than that to the same determinant coupled to a heterologous carrier. This and other evidence suggest an inverse relationship between humoral and cell mediated immunity. The purpose of this investigation was to explore the humoral response to antigens on cells which are syngeneic or allogeneic to the recipient, in order to determine the influence of a tolerated as opposed to allogeneic background. The approach used in this study was as follows: Mice were immunized with antigen (rabbit Fab' fragments) attached to syngeneic, allogeneic, or F₁ (semi syngeneic), irradiated spleen cells. Specific anti-rabbit Fab' plaque forming cell numbers were determined five days after the third, weekly injection of Fab' coated spleen cells. Some of the spleen cells taken from the responding animals, on the day of sacrifice, were incubated in vitro with soluble antigen (rabbit Fab' fragments not specific for mouse cells) for four days. The results showed that the humoral response to antigens attached to cells bearing 'self histocompatibility antigens (i.e. syngeneic or F₁ semi syngeneic cells) was significantly weaker than the humoral response to the same antigen on allogeneic cells. The effect of in vitro incubation of responder spleen cells for four days with soluble antigen was to reverse this difference. Those spleen cells exhibiting lowered plaque forming cell numbers initially (i.e. those cells from mice immunized with antigen on syngeneic or F₁ cell surfaces) showed, after incubation, a response equal to or greater than those cells which intially (before in vitro incubation) demonstrated a larger response (i.e. cells from those mice immunized with antigen on allogeneic cell surfaces). / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

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Antibodies specific for insulin and human immunoglobulin G (HlgG) were attached to controlled pore glass (CPG) particles which had been silanized with a diol-bearing silane. Up to 20 mg of antibody protein could be attached covalently to 1 gram of CPG. Such immobilized antibodies, or immunosorbents, would bind specific antigens, but not unrelated proteins, when used in a high pressure liquid chromatographic configuration. This technique was given the name "high performance immunoaffinity chromatography" (HPIC). The HPIC properties of these immunosorbents were evaluated by an equilibrium theory and were found to be comparable to batch values. An immunosorbent for HIgG antigen showed an HPIC association constant of 10⁷·⁶; the batch equilibrium constant for the same immunosorbent was 10⁷·⁸. Two different anti-insulin immunosorbents retained the intrinsic affinity (10⁶ and 10⁹) of the antibody used to make them. The total active antibody concentrations of these immunosorbents were evaluated by HPIC and batch methods with good agreement between the two. The immobilization reaction was seen to result typically in the loss of 90% of the original antibody activity. HPIC was shown to be applicable to the rapid analysis of antigens at levels as low as ng/mL. This was found to be possible in part because of the rapid forward kinetics which were assessed by HPIC. A forward rate constant of 3 X 10⁷ L·mol⁻¹·sec⁻¹ for the binding of insulin by a specific HPIC column could be determined. The possibility of HPIC fluorescence immunoassays was investigated using a highly sensitive fluorescence detector. An Eimac collimated xenon arc lamp provided sufficient power to detect picomolar levels of fluorescamine labeled insulin and other compounds. The limitations of HPIC in performing picomolar immunoassays were thus shown to be immunochemical rather than instrumental. The ability of immunoaffinity purifications to overcome these limitations was demonstrated.

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