Any aspect of the immune system can be deficient.  Which of the following deficiencies would primarily affect the BARRIER function of immunity? Group of answer choices A. Complement Deficiencies, in which a variety of complement proteins do     not  function properly B. DiGeorge Syndrome, in which the thymus does not develop properly C. Selective IgA deficiency, in which IgA antibodies are produced in very low amounts D. Severe Combined Immune Deficiency (SCID), in which all T and B cell functions are absent

Which of the following statements are true for antigen presentation.   a. Antigen presentation means that other cells attach the pathogen first and present it to T cells.   b. Antigen-presenting cells display protein fragments, resulting from the digestion of the pathogen, in complex with MHC receptor to B cells   c. Antigen presenting cells display protein fragments, resulting from the digestion of the pathogen, in complex with MHC receptor on their surface.   d. Antigen-presenting cells are phagocytic cells   e. Antigen presentation is required for T cell activation   f. Cytokines released by macrophages are required for T cell activation   g. T cell receptors recognize the MHC receptors in complex with antigen fragments displayed by antigen-presenting cells.   h. Phagocytic cells are involved in innate immunity. Therefore they have no role in T-cell activation

Antibodies Select one: a. are not specific, but act generally. b. are composed of four light and four heavy polypeptide chains. c. play a large role in cell-mediated immunity. d. are produced by both T and B cells. e. have a variable region that binds to a specific antigenic determinant.

Explain why each choice (a-d) is correct or incorrect. Allergens differ from antigens because a. Allergens produce an abnormally large immune response to what is an otherwise harmless particle. b. Allergens do not involve the leucocytes, they simple stimulate the inflammatory response. c. Allergens are only active seasonally and are generally harmless to the body. d. Allergens are primarily plant derived while antigens are bacterial or viral in nature.