Teddies Talks Biology - Issue 9

Continued

The glory soon wore off because the non - specific response knew that it could not de- feat this pathogen alone. A stronger force was needed; something bigger, stronger and more specific. This is when the specific im- mune system came to save the mans life. A macrophage which had digested a pathogen bound fragments of the bacterial antigens with a major histocompatibility complex pro- tein and this was displayed on the surface of the macrophage, so it became an antigen presenting cell. With a sense of urgency this macrophage migrated to a lymph node, hop- ing that it would find a T cell which could

solve all of their problems. Days went by but to the macrophage it had seemed like years, the man ’ s health was deteriorating, and the necessary T cell was still not found. Just when the APC thought all hope was lost, it felt something attach to its surface. There it was, the T cell with the complementary receptors! Without further hesitation the T cell was activated and divid- ed by mitosis to form clones of T helper cells, T killer cells and T memory cells. While all of this was happening, somewhere near the small intestine a B cell with complemen- tary antibodies had attached to and digested one of the bacteria. It also became an antigen presenting cell and began migrating to the lymph node. Once at the lymph node, the B cell waited patiently until finally it happened, an activated T helper cell with complementary recep- tors attached to the antigen presenting B cell and released cytokines. These cytokines activat- ed the B cell, initiating clonal selection in which the B cell divided to produce B effector cells and B memory cells. The effector cells quickly differentiated to become plasma cells. That day the rough endoplasmic reticulum and the Golgi apparatus of the plasma cells worked longer shifts than ever before, tirelessly transcribing, translating and modifying until they were releas- ing sufficient antibodies into the blood. These antigens were like the super medicine the man needed. A sense of hope was restored. The antibodies attached to the pathogens and forced them to clump together in the terror which was agglutination and the phagocytes ravenously digested them in large numbers. The bacteria ’ s game of hide and seek was put to a stop as the antibodies opsonised the bacteria, making them visible to the phagocytes who then feasted on the blood of the helpless salmonella bacteria. At the same time, cells which had already fallen to the bacteria were respectfully executed by their T killer cell comrades, knowing all to well that their death would be the only way that life could continue. With this in mind they sacrificed themselves without hesitation and saluted the T killer cells as the perforins began to take ef- fect, creating holes in their membranes and leading to the inevitable lysis of these brave cells. Finally, it looked like the battle had been won, the bacteria had been eradicated without mercy. Unfortunately, he body had also lost a fair few soldiers who lay in beds of white pus. The man felt better; his fever had lowered, the diarrhoea and the vomiting disappeared, and he no long- er felt nauseous. He had escaped the wrath of the salmonella on this occasion but who knows if he will escape again next time? Rest assured he will once again defeat the bacteria in any future battles because his body now has trained soldiers, ready to fight specifically these indi- gestible bacteria if they dare to return. The second battle will be legendary, an easy victory for the body, and the man will live to see another day.

Teddies Talks Biology I Issue 9 I June 2021

15