Characteristics of an antigen-adjuvant immunological complex in an experimental vaccine
formulation
Statement: The formulation of effective vaccines
generally requires adjuvants to stimulate an appropriate
immune response. Adjuvants are usually defined
as compounds that can increase or modulate
the immunogenicity of an antigen. According to the
literature, saponins are shown to possess several
physiological properties, mainly the capacity for
alteration of membrane permeability. These compounds
have been reported to possess therapeutic
potential for immune system modulation. Because
the observation that certain saponins cause substantial
enhancement of immune responses when
given together with an antigen in a vaccine, their
use as adjuvants received special attention. The
present study is concerned with the investigation
of molecular characteristics and structural aspects
of an antigen-adjuvant complex originated from an
experimental vaccine formulation. Methodology: A
commercial extract of Quillaja saponaria was fractionated
by chromatographic techniques to afford
a purified saponin (QS-21), which was identified by
Nuclear Magnetic Resonance spectroscopy. The adjuvant
potential of QS-21 on the cellular immuneresponse against ovalbumin antigen was evaluated.
The delayed type hypersensitivity reaction was used
as an in vivo assay of cellular immune response. The
capacity of the antigen-adjuvant complex to interact
with biomembranes was evaluated using in vitro assays.
Findings: When the immunization occurs only
with the antigen or the adjuvant without conjugation,
the cellular immune response was practically
abolished, since these compounds were not capable
to induce an effective immune response when administered
alone, which implies the necessity of conjugation
to elicit an immunological reaction, which
was significantly effective for the antigen-adjuvant
complex. Additionally, the complex showed a potent
capacity to interact with biomembranes, forming
structurally diverse aggregates. Conclusion: A remarkable
property of the antigen-adjuvant complex
to stimulate the immune response was demonstrated.
This activity can be attributed to its capacity to
form aggregates with biomembranes, identified as
the immunostimulating complexes, responsible for the enhanced immunogenicity
Author(s): Maria de Fatima Simao Juca Cri, Gabriela M Pereira, Elaine OR Viana, Marilia J da Silva, Bernadete P da
Silva and Jose P Parente
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