Final answer:
DiGeorge syndrome is associated with a defect in T cells, resulting in impaired immune function. Pollen allergy is categorized as immediate hypersensitivity (type I), which involves IgE mediating mast cell degranulation and is distinct from DiGeorge syndrome's immune defects.
Step-by-step explanation:
DiGeorge syndrome is primarily associated with a T cell defect. This condition results from a deletion on chromosome 22, leading to poor development of several body systems. Key issues in DiGeorge syndrome include defective immune system function, where both B and T cells can be defective, but it is the T cell deficiency that is most prominent. Immediate hypersensitivity, also known as type I hypersensitivity, involves IgE-mediated mast cell degranulation caused by crosslinking of surface IgE by antigen, which is different from the immune defects seen in DiGeorge syndrome.
Allergy to pollen is classified as immediate hypersensitivity (type I), not as an autoimmune reaction, immunodeficiency, or delayed hypersensitivity. Type II hypersensitivity reactions are mediated by antibodies leading to cell lysis (cytotoxicity), such as in Rh incompatibility, and are characterized by strong antibody reactions against antigens, different from the T cell-mediated reactions in type IV hypersensitivity.