Question

Antibodies to Trypanosoma Glycoprotein Variants Over Time Sleeping sickness is caused by the unicellular Trypanosoma parasite. The surface of this parasite is covered by glycoproteins that are encoded by a gene with more than 1,000 duplications in the trypanosome genome. Each of the gene copies is slightly different and has different molecular structures. The data below show the number of parasites over time (A) and the relative amount of antibodies specific to two trypanosome glycoproteins (B) over 24 days of a human infection, and the index varies from no antibodies (0) to many antibodies (1). Part A: Data from a Study of Parasite Levels Day Number of Parasites (in millions) per mL of Blood 0.1 0.3 1.2 0.2 0.2

Answer 1

The data in both the tables can be correlated as parasitic load vs antibody production by the immune system.In general terms, the parasitic load should decrease as the antibodies are produced. However, some deviation is observed as mentioned in the question. This could be attributed to the following-

Trypanosome Biology: The glycoproteins present on the surface of trypanosomal cells could be of variable nature. Glycoprotein A appears to be surface located and hence easily detected by the immune system. Thereby, antibody production is enhanced continuously. Whereas, glycoprotein b is embedded in the cell. In other words, it is hidden and escapes immune surviellance, thereby showing late antibody synthesis.

Adaptive Immune System:   Once, the antibodies synthesised against glyA neutalizes some cells, The disruption exposes glyB and then the recognition by Antigen Presenting Cells takes place. Once, they present antigen to T cells. T cell direct B cells to produce antibodies specific to gly B. Thus, taking more time.

Parasitic load increases after decreasing due to the time taken by the adaptive immune system to respond. Here, the rate of multiplying of parasite becomes more than antibody production. However, soon the immune system takes over and the load is decreased.