ABSTRACT
Modified-live, killed, and subunit vaccines have been developed to many different types of bacteria, including Mycobacterium tuberculosis, Escherichia coli, Haemophilus, pneumococcus, Vibrio, Helicobacter (ulcer-causing bacteria), and the Lyme disease spiro-chete. Most familiar is the diphtheria, pertussis, and tetanus (DPT) vaccine that many young children receive to protect them from often fatal childhood diseases. Some bacterial vaccines induce antibodies specific for proteins on the bacteria required for their attachment and subsequent invasion of the host; others induce immunity to endo- or exotoxins. BCG, which protects against tuberculosis, is most effective against the miliary form of this disease as well as tuberculous meningitis. T-independent vaccines to carbohydrates such as the capsule of pneumococcus or Haemophilus are effective but have limitations because T-cell help is not provided for affinity maturation and isotype switching. However, a “conjugate” vaccine with pneumococcal carbohydrates attached to diptheria toxoid is available that allows the development of IgG antibodies of high affinity.
