c. Antibody dependent cellular phagocytosis

Similarly, antibody-dependent phagocytosis a virally infected cell is recognized by

an antibody and the phagocyte recognizes the antibody (not the cell) and phago-

cytoses the cell.

3.3.2

CELL-MEDIATED RESPONSE

3.3.2.1

T-Cell Recognition

Each T-cell has a T-cell receptor, and each T-cell receptor recognizes a different

epitope of an antigen. T-cell receptors, similar to antibodies, recognize an antigen

with very high specificity. As shown in Figure 3.11, the T-cell receptor is made up

of two 43 kDa chains, α and β, held together by a disulfide bond. Each chain spans

the plasma membrane and has a short cytoplasmic tail. Much like the heavy and

light chains making up antibodies, α and β chains also possess variable and constant

regions and the antigen-binding region is made up by the variable region.

3.3.2.2

Helper T-Cells

The next phase of immune activation takes place in the lymph node, which is re-

presented diagrammatically in Figure 3.6. As discussed earlier, B-cells become

activated upon antigen-binding. This triggers a number of events starting with their

FIGURE 3.10 Antibody-dependent cellular cytotoxicity. Cells expressing antigens on their

cell surface that are recognized by antibodies are the targets of antibody-dependent cellular

cytotoxicity, when the Fc portion of the antibody is bound by specific receptors on NK cells.

This triggers the release of perforin that generates pores in the membrane of the target cell,

allowing the entry of granzyme, an apoptosis-causing molecule.

46

Bioprocessing of Viral Vaccines