Researchers at the University of California have recently made a discovery that could be used to develop a vaccine against the highly infectious group A Streptococcus (GAS) bacteria.
According to the CDC, GAS causes a variety of infections ranging from relatively mild illnesses such as strep throat to life-threatening illnesses such as pneumonia or necrotizing fasciitis (a disease that destroys the body’s tissue).
When the body is infected, it recognizes and attacks the invading germs using antibodies. The antibodies recognize a specific part of the germ called an antigen.
The antigen allows antibodies to specifically target the invading germ without hurting the rest of the body. Vaccines work by introducing the body to certain antigens without causing an infection. The body fights these antigens and then remembers how to fight the antigen in the future should the actual infection present itself. Therefore, vaccines allow the body to respond more quickly to an antigen, which prevents the disease from spreading.
The problem with GAS is that the bacteria have many different types of strains, each with a different type of antigen, called an M protein. Currently, there are over 200 different M proteins known. An antibody usually recognizes a region known as the hypervariable region (HVR) in the M protein. However, since there are many hypervariable regions, antibodies can only provide limited protection for specific strains. Therefore, it is difficult for researchers to develop one vaccine to target multiple types of GAS bacteria.
The researchers discovered that a specific protein, human C4b-binding protein (C4BP), recognizes many (about 90 percent) M protein HVRs. C4BP is used by the M proteins to suppress the body’s immune system. The researchers were interested that one protein could recognize and be used by so many different types of GAS bacteria, so they decided to study what made the C4BP protein able to be recognized by hundreds of diverse GAS strains.
Proteins are made up of smaller subunits called amino acids. The order, or sequence, of amino acids determines the identity, shape and function of each protein. To determine what made C4BP nearly universally recognizable, researchers examined the structure of C4BP and its interactions with different types of M proteins. They discovered that there is a pattern of recognition between the M proteins and C4BP.
Though the M proteins seemed to be unrelated, they shared some sequential similarities (some amino acid sequences remained the same throughout all the M proteins). It is through these similar sequences that C4BP recognizes the many different M proteins and, therefore, the many different GAS bacteria strains.
Researchers hope to use this new knowledge to make a vaccine that will target similar sequences that C4BP targets. This vaccine will have an antibody that binds to the GAS antigen (M protein) in a way similar to the way in which C4BP binds to the M protein. They are hopeful that this vaccine will confer a broad immunity to many different types of GAS bacteria, which will protect people against almost all strains of GAS.