Page 116 - Biology Form Two

Biology for Secondary Schools

then enters the cell. Once inside the cell, the virus becomes part of the T-helper
cell and replicates together with it as it undergoes division. This increases the
number of HIV in the blood. The HIV destroys T-helper cells resulting in the
reduction of the number of T-helper cells and reducing the CD4 count. Figure
5.11 shows HIV attacking the T-helper cell.
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HIV

HIV attach to CD4 of T-helper cell

T-helper cell

CD4

Figure 5.11: HIV attacking the T-helper cell

HIV destroys T-helper cells in the cell. A giant cell can survive but
following ways: it cannot perform normal T-helper
(i) it reproduces inside the T-helper cell functions.

cell and then ruptures the cell’s
membrane and the new viruses Thus, HIV lowers the body’s immunity
are released; to a great extent making it vulnerable
to opportunistic infections.
(ii) it alters the T-helper cell so that
when it responds to an infection, Platelets
it kills itself instead of dividing to Platelets are small fragments of cells
form new cells; produced in the bone marrow. They are

(iii) it marks T-helper cells as targets also known as thrombocytes (Figure
for destruction by other cells in 5.12). They do not have nuclei and
the immune system; and cannot reproduce.

(iv) it causes the fusion of many
T-helper cells to form a ‘giant’

110 Student’s Book - Form Two

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