Role of antibodies in the prevention and treatment of Cryptococcus neoformans

Abstract

Encapsulated organisms, such as Streptococcus pneumoniae, Haemophilus influenzae type B, Neisseria meningitidis, group B streptococcus and Cryptococcus neoformans are extremely important clinically because they are responsible for many serious infections and for most deaths from meningitis. Data presented in this thesis describe the work done to further our understanding of two separate issues: (1) to generate a vaccine that would induce immunological memory (T-cell dependant) and focus the immune response against only protective epitope(s) of glucuronoxylomannan (GXM); and (2) to study the mechanisms behind antibody protection and enhancement.;Peptides that specifically react with 2H1, a protective mAb to GXM were isolated from peptide phage display libraries, and their efficacy as peptide mimotope vaccines were studied. Peptide P206 has a high affinity for 2H1, yet was unable to generate a significant anti-GXM antibody response in naive mice. Different immunization protocols were developed using P206 as a secondary reagent to focus the immune response to a protective epitope. Mice first primed with GXM-TT and boosted with P206-conjugated to keyhole limpet hemocyanin (KLH) developed significant titers to GXM, yet the antibodies were not focused onto a protective epitope and infection in these animals was enhanced. However, animals primed with a low dose of GXM-TT and boosted with peptide P206 conjugated to tetanus toxoid (TT) developed significant titers to GXM that were focused onto a protective epitope.;The effect of the carrier protein on the protective efficacy of our peptide vaccines was further characterized. Peptide mimetics of GXM conjugated to KLH with glutaraldehyde elicit a slight antibody response to GXM in mice. However, control peptides P315 and P24A conjugated to KLH, also elicited a response to GXM. GXM binding antibodies from mice immunized with P315-KLH were inhibited by KLH treated with glutaraldehyde (KLH-g) but not by P315. Furthermore, KLH-g inhibited the binding to GXM by serum of mice immunized with GXM-TT, indicating that glutaraldehyde treatment of KLH reveals an epitope that cross-reacts with GXM.;Mice passively immunized with 3E5 IgG3 anti-GXM mAb have an enhanced cryptococcal infection, whereas the other 3E5 IgG isotypes can prolong the life of infected animals. This, in addition to other findings, point to the existence of a putative IgG3 FeR which could participate in the enhancement of C. neoformans infection. Rat mAbs that inhibit the binding and phagocytosis of IgG immune complexes to effector cells have been generated. (Abstract shortened by UMI.).