👎🏻A is not correct. A dimeric compound held together by a J chain is an IgA antibody. These secretory molecules are found in mucosal surfaces such as the gastrointestinal tract and the oropharynx. Although this patient most likely fought the original Streptococcus infection with these antibodies, they do not participate in the presentation of antigens to the immune system.
👎🏻C is not correct. The complex described here is the major histocompatibility class (MHC) I, a presenting compound of intracellular pathogens. They are present on all nucleated cells in the body and constantly display to the outside world what proteins they are currently producing. In case of viral infection or a malignant process, CD8+ cells are activated by the unknown peptide now displayed on the MHC I molecules and proceed to kill the cell. MHC I compounds play no role in the processing of extracellular pathogens, as is the case in this patient.
👎🏻D is not correct. Two heavy (H) and 2 light (L) chains are the basic structure of all monomeric antibodies. In the sequelae of a streptococcal throat infection, these antibodies, which originally were formed to bind to streptococcal proteins (specifically M protein), now damage tissues in the body with similar surface molecules. Antibodies are produced as a consequence of antigen presentation but do not participate in it.
👎🏻E is not correct. The molecule described here is the CD4 surface marker. The CD4 surface marker is crucial for recognition of the major histocompatibility class II complex by the T-cell receptor. Although it is important in the process of antigen presentation, the CD4 molecule is not the compound actually displaying the fragment of the pathogen.
👎🏻C is not correct. The complex described here is the major histocompatibility class (MHC) I, a presenting compound of intracellular pathogens. They are present on all nucleated cells in the body and constantly display to the outside world what proteins they are currently producing. In case of viral infection or a malignant process, CD8+ cells are activated by the unknown peptide now displayed on the MHC I molecules and proceed to kill the cell. MHC I compounds play no role in the processing of extracellular pathogens, as is the case in this patient.
👎🏻D is not correct. Two heavy (H) and 2 light (L) chains are the basic structure of all monomeric antibodies. In the sequelae of a streptococcal throat infection, these antibodies, which originally were formed to bind to streptococcal proteins (specifically M protein), now damage tissues in the body with similar surface molecules. Antibodies are produced as a consequence of antigen presentation but do not participate in it.
👎🏻E is not correct. The molecule described here is the CD4 surface marker. The CD4 surface marker is crucial for recognition of the major histocompatibility class II complex by the T-cell receptor. Although it is important in the process of antigen presentation, the CD4 molecule is not the compound actually displaying the fragment of the pathogen.