Conjugated vaccine

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A conjugate vaccine ( latin conjugatio , Union ') is a vaccine in which the antigen - consisting for example (parts of the capsule of bacterial envelope polysaccharides to a protein (-) of a pathogen protein is bound). Conjugated vaccines are able to generate a stronger and longer lasting immune response compared to the unconjugated antigen. In particular, the immune system of infants and young children is not yet mature enough to develop efficient antibodies against non-protein antigens such as polysaccharides, lipids or nucleic acids .

Conjugate vaccines are the Hib and meningococcal C vaccines. The pneumococcal vaccine is available as 7, 10 and 13-valent conjugate vaccines and in a 23-valent non-conjugated variant.

Mechanism of action

Foreign polysaccharides and lipids generally trigger a weaker immune response in the body , as these are mainly recognized and eliminated by the mechanisms of the innate immune system . They do not bind to MHC and do not trigger a reaction in T cells , but as T cell-independent antigens they can activate B cells. Due to the short biological half-life, there is hardly any long-term immunity that can be caused by an adaptive immune response ( humoral and cellular immune response ). In addition to the capsular polysaccharides, haptens are also coupled to a carrier protein to increase their immunogenicity . The formation of T H 2 lymphocytes, specific antibodies by plasma cells and B memory cells are often not triggered with unconjugated antigens. Since the antigens are hardly taken up in cells, there is also only a low presentation at MHC I and only a low antigen-specific cellular immune response.

For B-cell differentiation, most antigens require T-helper cells of the T H 2 type to further stimulate the immature B-cells so that they develop into plasma and memory cells. In order to bring about a corresponding T-cell participation, the antigen must be a protein or protein fragment which can be presented to the CD4-positive T-helper cells by the phagocytic B-cell, with the help of its MHC II molecule on the cell surface. These bind to the naive B-cell with the help of special surface molecules, among other things CD4-positive T-cells recognize the MHC-II of the antigen-presenting B-cell. A second receptor , CD28 , mediates the binding to the B-cell costimulator B7. Third, the CD40 ligand binds to the CD40 receptor of the B cell.

In T H 2 cells, the T cell receptor (TCR) binds to the antigen. As soon as this bond is established, messenger substances ( cytokines ) are secreted by the CD4-positive T cell , which give the B cell the final signal for differentiation . This creates a new generation of plasma cells that produce specific antibodies and thus trigger a stronger immune response. In addition, B memory cells are formed which, in the event of a reinfection, can trigger a stronger and faster immune reaction and thus lead to longer-term immunity .

With the help of a conjugated vaccine one is accordingly able to generate a stronger and long-term effective immunity compared to the unconjugated antigen. The immune system of infants and small children is still developing, which is why, for example, the usual 23-valent pneumococcal vaccination is not used in this age group , but a 7-, 10- or 13-valent conjugate. Other conjugate vaccines are used against meningococci and Haemophilus influenzae type b , among others .

literature

  • Heinz Spiess, Ulrich Heininger: Vaccination Compendium . 6th edition. Thieme, Stuttgart 2005, ISBN 978-3-13-498906-9 .

Individual evidence

  1. ↑ F. Destefano, D. Pfeifer, H. Nohynek: Safety profile of pneumococcal conjugate vaccines: systematic review of pre- and post-licensure data . In: Bull World Health Organ . (2008), Vol. 86 (5), pp. 373-80. PMID 18545740 ; PMC 2647448 (free full text).
  2. ^ GA Poland: Prevention of meningococcal disease: current use of polysaccharide and conjugate vaccines. In: Clin Infect Dis . (2010), Vol. 50 Suppl 2, pp. 45-53. PMID 20144016 .
  3. ↑ DF Kelly, ER Moxon, AJ Pollard: Haemophilus influenzae type b conjugate vaccines. In: Immunology (2004), Vol. 113 (2), pp. 163-174. PMID 15379976 ; PMC 1782565 (free full text).