antigenic hybrids - refers specifically to HA/NA hybrids in which genes for the coding of these 2 surface proteins are derived from different viruses as the result of genetic reassortment. In many such reassortants listed in this archive one or the other gene has been derived from an animal virus subtype alien to human experience, e.g., H7N7. In this case, an H7N2 reassortant is said to be essentially "NA-specific" when used as an immunizing antigen or as a test reagent, and conversely, an H3N7 reassortant might be "HA-specific".

genotype - for most of the viruses in this archive the "genotype" is defined indirectly by the antigenic phenotype of the virus - the HA and NA proteins. Where further information is available - either by identification directly or indirectly of the genes for the internal or M1 proteins - it is specifically given, or the method of genotyping, e.g., PAGE, is given.

H - high yield HA mutants specifically of contemporary swine H1N1 influenza viruses related to single base changes in the HA gene.

HA - hemagglutinin, the dominant surface antigen of the influenza virion and principal mediator of immunity. Together with the NA (neuraminidase) it defines the antigenic phenotype of the virus, which in turn, classifies the influenza A viruses into subtypes.

HI - hemagglutination-inhibition test (or titer) - measures antibody to the hemagglutinin (HA) by inhibition of the binding of virus to red blood cells (RBC).

hr - host range mutants - anomalous host system should be specified - e.g., MDBK cells.

hy - (high yield) - virus has high-yielding properties in the chick embryo as measured by hemagglutination titrations (which essentially measure total virus: infective, inactivated, and non-infective virus particles). This phenotype is critically important for vaccine production (see "Vaccine Candidate", below).

L - low yield HA mutants specifically of contemporary swine H1N1 influenza viruses related to single base changes in the HA gene.

ma - (mouse adapted) - virus will produce weight loss, lung lesions and/or death after intranasal (i.n.) inoculation of mice.

N - (neurotropic) as in NWS and WSN. Virus replicates and causes lesions in mouse brain after intracerebral (i.c.) inoculation.

NA - neuraminidase, an antigen with enzymatic function on the virion surface with an important but secondary role in the induction of immunity to influenza.

NI - neuraminidase-inhibitions test (or titer) - measures antibody directed against the neuraminidase (NA) enzyme by specific inhibition of NA enzymatic activity.

phenotype - defined principally by the HA and NA proteins, but also by biologically manifest properties of the virus such as inhibitor sensitivity, etc.

ts+ - (temperature sensitive) - applied to mutants that cannot replicate at 39°C.

vaccine candidate - a reassortant virus containing the HA and NA proteins of a virus of potential epidemiologic importance used in the reassortment process with A/PR/8/34 and containing the PR8 RNA 7 (M gene) that is associated with the hy phenotype.

wt - (wild type) or native virus not yet subjected to lab manipulation (as opposed to a selected mutant or reassortant virus).

X series reassortants - An arbitrary numerical system of nomenclature established within the Kilbourne laboratory as a convenient method of distinguishing reassortants from wild type viruses without the need for using a cumbersome combination of the 2 parental names. The X viruses are chiefly those produced as vaccine candidates or as test reagents. In general, (but unfortunately with some exceptions) odd-numbered reassortants have the HA/NA phenotype of the newly emergent wt parent and have acquired the RNA 7 coding for the M gene in A/PR/8/34 virus which has been linked to the capacity of a virus to replicate to high yield (hy) in the allantoic sac of the chick embryo. Such hy reassortants are all provisional "vaccine candidates" for use in production, with their use being dependent on the epidemiological prevalence of the new strain. In general, even-numbered "X" reassortants are HA/NA antigenic hybrids in which the NA is derived from the new wild type virus and the HA ("carrier") from an animal virus such as H7N7, e.g., H7N2, or X-22. The reverse HA-specific hybrid H3N7 is often identified as X-22(R). In the individual virus files the specific antigenic composition is given, in any case. (The hy reassortants similar in phenotype to wt virus would be odd numbered, e.g., X-21).