In studies of skin grafts, thymectomized mice (their thymus has been removed) are often used

You have a patient with abnormally high IgE antibodies. What are two scenarios that might lead to a high level of IgE antibodies? How would you find out which scenario is causing the increase in IgE?

The immune system involves both the humoral and cell-mediated branches. It is known that T cells can perform a range of different functions once selected by antigen encounter, including secretion of soluble compounds to aid other white blood cells, such as B lymphocytes. If T cells can aid the function of B lymohocytes, then is it incorrect to say that both branches of the immune system (humoral and cell-mediated) involves B cells? I ask this question because I commonly hear that humoral immunity involves B cells rather than both branches.

Infants and young children with deficiencies in specific complement components present with recurrent respiratory infections caused by extracellular bacteria. The peak age of susceptibility is between 6 and 12 months after birth. At this time, as shown in figure below, maternal antibodies acquired by the child during fetal gestation are nearly gone, but the child is not yet generating robust antibody responses to new infections, as indicated by the low circulating levels of IgG and IgA. As children with this immunodeficiency get older, they outgrow this disease and show no further evidence of these recurrent infections. Based on this information, name one likely gene deficiency (in the complement system) that could cause this primary immunodeficiency, and the specific complement pathway likely to be affected. Explain your answer.