All exposed to H1N1 flu have developed antibodies: NIV study
Umesh Isalkar, TNN 10 September 2009, 12:08am IST
PUNE: As per the findings of a study conducted by scientists at the National Institute of Virology (NIV), over one lakh people were exposed to the
H1N1 A influenza virus and "all of them have developed antibodies against the novel H1N1 strain," A C Mishra, director of NIV, told TOI on Wednesday.
"There is no denying the fact that the extensive exposure of the city's population to the H1N1 virus has led to building immunity against it," Mishra said.
Notably, the NIV had conducted a serological study of 1,000 doctors to find out whether they had developed antibodies against the virus. "We found that a few of them had developed antibodies against the H1N1 virus, but going by our recent study, we have come to the conclusion that over one lakh people were exposed to the H1N1 virus in the city and all of them had developed immunity against it," Mishra said.
Asked why the presence of antibodies was found in certain doctors only, Mishra said, "The development of antibodies differs from group to group. Earlier, the small group studied comprised only doctors, but this time, we are talking about the population in general."
Asked whether the exposed people could still get infected at a later stage, Mandeep Chadha, deputy director of NIV, said, "They may not get infected with the specific strain to which they were exposed for a long time."
When contacted, microbiologist Siddharth Dalvi said, "Since a large number of people in the city had been exposed to the H1N1 influenza, they must have developed immunity in the form of antibodies and cytotoxic cells." Elaborating, Dalvi said there are two types of immune responses antibody-mediated and cell-mediated. "Antibodies are special proteins that react specifically with a particular foreign target, for example, proteins of bacteria or viruses," he said. "Antibodies are produced after an individual encounters a foreign protein. Depending on several factors, the antibody remains in the system for a few weeks to several years. In case of certain viruses, it may even persist lifelong," Dalvi said.
Influenza virus has 10 types of proteins and antibodies are produced against most of these. "However, only those antibodies produced against the surface proteins (hemagglutinin and neuraminidase) provide protective immunity. On the other hand, antibodies produced against internal viral proteins do not provide protection, but can be used for diagnosis of influenza," Dalvi said.
Sharing the view, virologist Sonali Sanghavi said, "A majority of antibodies are present in the bloodstream in the form of freely circulating molecules. A certain type of antibody (called IgA) is present in the nasal secretions, that is, locally in the respiratory tract and provides protection against infection."
"Certain special cells of the immune system called T cells also play a role in protective immunity. The T cells have a central role in defence against the influenza virus as they can directly kill the virus-infected cells as well as promote antibody formation," said Sanghavi. Optimum protection against influenza infection requires co-ordinated effort by the local antibody, circulating antibody and the T cells, Sanghavi said.
