In developed countries, an enormous change has occurred within the human body over the past century—the loss of parasitic worms. Due to improvements in sanitation, roundworms that have inhabited human intestines (such as the hookworm above) and challenged our immune system for millions of years are no longer a threat. Does the end of this long-term relationship come at a cost?What is the hygiene hypothesis? What correlation does it attempt to explain?

Which of the following outcomes would be expected if somatic hypermutation did not occur?a. The diversity of pattern-recognition receptors would be significantly lowered.b. B and T lymphocytes would not be able to produce receptors thatrecognize antigens.c. The adaptive immune response would not be activated by pathogens.d. The secondary immune response to a repeat infection would produce the same antibodies as those made in the primary immune response.

Which of the following statements is not true?a. An antibody has more than one antigen-binding site.b. An antigen can have different epitopes.c. A lymphocyte has receptors for multiple and different antigens.d. A bacterium has more than one antigen.

Propose a hypothesis to explain how self-reactive B cells are identified and eliminated during maturation.

Propose an explanation for why we need a flu shot year after year, instead of only once early in life.

SCIENTIFIC THINKING Pertussis (whooping cough) is caused by a bacterial infection, and symptoms include an intense cough that lasts for weeks, sometimes leading to pneumonia and death. A complete vaccination against pertussis requires five doses, completed by age 5. A pertussis outbreak occurred in California in 2010, and a news article reported the following: 'Among fully immunized kids, there were about 36 cases for every 10,000 children two to seven years old, compared to 245 out of every 10,000 kids aged eight to twelve.' Propose an explanation for these data and a public health solution based on your explanation.

In developed countries, an enormous change has occurred within the human body over the past century—the loss of parasitic worms. Due to improvements in sanitation, roundworms that have inhabited human intestines (such as the hookworm above) and challenged our immune system for millions of years are no longer a threat. Does the end of this long-term relationship come at a cost?Explain how the adaptive and innate immune responses work together to defend the human body against infection by parasitic worms.

Your roommate is rushed to the hospital after suffering a severe allergic reaction to a bee sting. After she is treated and released, she asks you (the local biology expert!) to explain what happened. She says, 'I don't understand how this could have happened. I've been stung by bees before and didn't have a reaction.' Suggest an explanation for what has happened to cause her severe allergic reaction and why she did not have the reaction after previous bee stings.

In developed countries, an enormous change has occurred within the human body over the past century—the loss of parasitic worms. Due to improvements in sanitation, roundworms that have inhabited human intestines (such as the hookworm above) and challenged our immune system for millions of years are no longer a threat. Does the end of this long-term relationship come at a cost?Pattern-recognition receptors have been identified that recognize worm products. Explain how these receptors are used to activate the adaptive immune response most appropriate for worm infection.