GATE 2019 BT Q.34: solution and answer

Official answer: BSource: Official answer key, GATE 2019 BT (IIT Madras)

1. A hybridoma is a hybrid cell line made to give a continuous supply of one monoclonal antibody (the Kohler and Milstein technique).

2. Antibody production is the property of B lymphocytes (plasma cells), so the antibody-producing partner must be a B cell, usually taken from the spleen of an immunised animal.

3. A normal B cell cannot divide indefinitely in culture, so it is fused with an immortal myeloma (B-cell tumour) cell, which supplies unlimited growth.

4. The myeloma partner is chosen to be deficient in HGPRT and to secrete no antibodies of its own. In HAT medium the unfused myeloma cells die because they cannot use the salvage pathway, and the unfused B cells die because they have a limited life span in culture. Only the fused hybridoma cells survive.

5. Option (A) is wrong: T cells do not make antibodies. They carry T cell receptors and regulate immunity.

6. Option (C) is wrong: macrophages present antigen and phagocytose, but they do not secrete antibodies.

7. Option (D) is wrong: both partners are normal, mortal lymphocytes. A fusion of a T cell and a B cell has no immortal partner, so it would not form a stable, indefinitely growing antibody-secreting line.

8. Therefore the antibody-producing hybridoma arises from fusing a B cell with a myeloma cell, option (B).