Question

B cells are activated by CD4 TH2 cells only if both cell types recognize the same antigen. The same epitope, however, does not need to be shared for recognition.

1. Discuss why this characteristic is important in vaccine design.

2. Provide an example of a conjugate vaccine used to stimulate the synthesis of IgG antibody against Haemophilus influenzae B polysaccharide.

Answer 1

Answer1

This phenomenon is referred to as linked recognition and is applied widely in designing vaccines, like that used to immunize infants against Haemophilus influenzae type B. Generation of T cell memory is fundamental in designing such vaccines, which offer long-term protection against seasonal and pandemic viruses. The reason for this is basically the ability of these cells to generate secondary immune responses. Secondary effector CD4 T cells are superior to primary effectors as well as to resting memory cells (shown via an adoptive transfer system). The efficiency comes in terms of IL-4 production and providing immunoglobulin G responses. Thus, memory cells give increased level of assistance as compared with naïve cells and their helping capacity can be increased during the kinetic development of recall responses.

H.influenza is a pathogen that can infect brain lining / meninges to cause a condition called meningitis. In severe cases, the infection also leads to neurological damage or death. To stop this pathogen, antibodies mediated against its capsular polysaccharide are designed. In adults, effective thymus-independent responses to these polysaccharide antigens can happen, but not in immature immune system of infants. To have effective vaccines working in infants, the bacterial polysaccharide is linked chemically to tetanus toxoid, a foreign protein against which infants are routinely vaccinated. B cells bind to the polysaccharide component of the vaccine and are activated by helper T cells specific for peptides of the linked toxoid. Those B cells that do not bind to the polysaccharides are not activated.

Answer2

Haemophilus influenza type B Polysaccharides-protein conjugate vaccine:

Three Haemophilus influenza type b (Hib) conjugate vaccines namely PRP-meningococcal outer membrane protein complex (PRP-OMPC), PRP-non toxic mutant diphtheria toxin, CRM 197 (HbOC) and PRP-tetanus toxoid (PRP-T) can elicit IgG response. Hib coupled to an outer membrane protein of group B Neisseria meningitidis is a conjugate vaccine which elicits IgG1 and IgG2, but higher IgG1 response.