Which type of hypersensitivity involves IgG or IgM antibodies reacting with host cell membranes?

Type II hypersensitivity is characterized by the involvement of IgG or IgM antibodies that specifically target antigens on the surface of host cells. This type of hypersensitivity reaction occurs when these antibodies bind to the antigens, leading to various pathological effects such as cell lysis, phagocytosis, or inflammation. The binding of antibodies to host cell membranes can result in conditions like autoimmune hemolytic anemia, where red blood cells are destroyed due to the action of these antibodies.

In contrast, Type I hypersensitivity involves an immediate allergic reaction mediated by IgE antibodies and is primarily associated with allergens, leading to conditions such as asthma and anaphylaxis. Type III hypersensitivity reactions are the result of immune complexes formed by IgG or IgM antibodies and soluble antigens, which can deposit in tissues and cause inflammation, but this does not directly involve the reaction with host cell membranes. Type IV hypersensitivity is a delayed-type reaction mediated by T cells and does not involve antibodies at all.

Therefore, the defining characteristic of Type II hypersensitivity is indeed the reaction of IgG or IgM antibodies with antigens on host cell membranes, making this the correct answer.