Question XI Many opsonins are multimeric as opposed to monom

Question XI. Many opsonins are multimeric (as opposed to monomeric) molecules [complete the sentence and assess the resulting statements (118-123) describing various hypothetical conclusions as either factually correct (= “true”) or incorrect (= “false”)]:

118. so that they can be regulated allosterically.

119. because they are all derived from the same proto-opsonin.

120. and, therefore, their phagocytosis-inhibiting activities are reduced.

121. – one subunit binds pathogen and the other has enzymatic activity.

122. and thus can bind repeating structures on pathogen surfaces.

123. because they have to crosslink receptors on phagocytes in order for phagocytosis to occur

Solution

ANS:

True statement:

122. and thus can bind repeating structures on pathogen surfaces.

Explanation:

Opsonin is a phagocytosis promoting substance or antibody, which binds on the surface of foreign microorganisms and causes cell lysis. Opsonin binding on microorganism’s surface is mediated by 2 pathways.

Opsonin dependent: It is mediated by antibody or C3b recognized by phagocytes.

Opsonin indedependent: It is mediated by variety of specific and non-specific receptors on phagocytes lectin – carbohydrate binding protein protein-protein binding.

False statements:

118. so that they can be regulated allosterically.

119. because they are all derived from the same proto-opsonin.

120. and, therefore, their phagocytosis-inhibiting activities are reduced.

121. – one subunit binds pathogen and the other has enzymatic activity.

123. because they have to crosslink receptors on phagocytes in order for phagocytosis to occur

The statement 120 (and, therefore, their phagocytosis-inhibiting activities are reduced) is not completely true. Phagocytosis is promoted by several immunological cells, not only with opsonin. So these cells in immune system can able to reduce phagocytosis-inhibiting activities.

Opsonisation:

Macrophages express Fc R receptor, complement receptor to which Ig G coated with antigen, C3b coated with antigen bind to the respective receptor and increases a phagocytic activity process known as opsonisation.