1. Injections of TC cells completely removed all Hepatitis B viruses from infected mice, but the injections killed only 5% of the infected liver cells. Explain how TC cells cured the mice.

TC cells or T cytotoxic cells have the ability to recognize kill target cells that are nonself. These target cells are self-cells that have been altered by infection with a pathogen, especially viruses such as Hepatitis B. They carry parts of endogenous antigens on its surface and are synthesized within a cell. More so, a normal cell will not trigger a response by a CTL but a virus infected cell produces abnormal endogenous antigens. The abnormal antigen attaches to the surface of the cell. In its attack, a CTL binds to the target cell and releases perforin. As a result the CTL induces destruction of the virus-infected cell by programmed cell death.

2. A patient with AIDS has a low TH cell count. Why does this patient have trouble making antibodies? How does this patient make any antibodies?

Patients with AIDS have a low TH cell count because their immune system is being attacked on a constant basis. “This virus however, can also infect other cells, which include macrophages and certain other kinds of cells, which can engulf substances through a process known as phagocytosis. As a consequence of the interaction with CD4 on helper T-cells, HIV specifically infects the very cells necessary to activate both B-cell and cytotoxic T-cell immune responses. Without helper T-cells, the body cannot make antibodies properly, nor can infected cells containing HIV (an intracellular pathogen) be properly eliminated. Consequently, the virus can: multiply, kill the helper T-cell in which it lives, infect adjacent helper T-cells, repeat the cycle, and on and on, until eventually there is a substantial loss of helper T-cells” (Brown, 2007).

3. Newborns (under 1 year) who contract