Newcastle disease virus and two influenza viruses: differing effects of acid and temperature on the uptake of infectious virus into bovine and canine kidney cell lines

Temperature dependent viral tropism: understanding viral seasonality and pathogenicity as applied to the avoidance and treatment of endemic viral respiratory illnesses

This review seeks to explain three features of viral respiratory illnesses that have perplexed generations of virologists: (1) the seasonal timing of respiratory illness and the rapid response of outbreaks to weather, specifically temperature; (2) the common viruses causing respiratory illness worldwide, including year‐round disease in the Tropics; (3) the rapid arrival and termination of epidemics caused by influenza and other viruses. The inadequacy of the popular explanations of seasonality is discussed, and a simple hypothesis is proposed, called temperature dependent viral tropism (TDVT), that is compatible with the above features of respiratory illness. TDVT notes that viruses can spread more effectively if they moderate their pathogenicity (thereby maintaining host mobility) and suggests that endemic respiratory viruses accomplish this by developing thermal sensitivity within a range that supports organ‐specific viral tropism within the human body, whereby they replicate most rapidly at temperatures below body temperature. This can confine them to the upper respiratory tract and allow them to avoid infecting the lungs, heart, gut etc. Biochemical and tissue‐culture studies show that ‘wild’ respiratory viruses show such natural thermal sensitivity. The typical early autumn surge of colds and the occurrence of respiratory illness in the Tropics year‐round at intermediate levels are explained by the tendency for strains to adapt their thermal sensitivity to their local climate and season. TDVT has important practical implications for preventing and treating respiratory illness including Covid‐19. It is testable with many options for experiments to increase our understanding of viral seasonality and pathogenicity.

Seasonality and selective trends in viral acute respiratory tract infections

Influenza A and B, and many unrelated viruses including rhinovirus, RSV, adenovirus, metapneumovirus and coronavirus share the same seasonality, since these viral acute respiratory tract infections (vARIs) are much more common in winter than summer. Unfortunately, early investigations that used recycled “pedigree” virus strains seem to have led microbiologists to dismiss the common folk belief that vARIs often follow chilling. Today, incontrovertible evidence shows that ambient temperature dips and host chilling increase the incidence and severity of vARIs. This review considers four possible mechanisms, M1 - 4, that can explain this link: (M1) increased crowding in winter may enhance viral transmission; (M2) lower temperatures may increase the stability of virions outside the body; (M3) chilling may increase host susceptibility; (M4) lower temperatures or host chilling may activate dormant virions. There is little evidence for M1 or M2, which are incompatible with tropical observations. Epidemiological anomalies such as the repeated simultaneous arrival of vARIs over wide geographical areas, the rapid cessation of influenza epidemics, and the low attack rate of influenza within families are compatible with M4, but not M3 (in its simple form). M4 seems to be the main driver of seasonality, but M3 may also play an important role.

Insights into neutralization of animal viruses gained from study of influenza virus

It has long been known that the binding of antibodies to viruses can result in a loss of infectivity, or neutralization, but little is understood of the mechanism or mechanisms of this process. This is probably because neutralization is a multifactorial phenomenon depending upon the nature of the virus itself, the particular antigenic site involved, the isotype of immunoglobulin and the ratio of virus to immunoglobulin (see below). Thus not only is it likely that neutralization of one virus will differ from another but that changing the circumstances of neutralization can change the mechanism itself. To give coherence to the topic we are concentrating this review on one virus, influenza type A which is itself well studied and reasonably well understood [1–3]. Reviews of the older literature can be found in references 4 to 7.

Cell type specific expression and regulation of murine interferon alpha and beta genes

The differential and cell type specific expression of various murine IFN alpha genes and IFN beta was examined by S1 nuclease protection assays in M-CSF cultured C57BL/6 mouse bone marrow macrophages and L929 fibroblasts. In Newcastle disease virus (NDV) induced macrophages, IFN beta, alpha 2, alpha 4, and alpha 1 mRNAs were the predominant species, whereas IFN alpha 6 and alpha 9 transcripts accounted for only 5% of total IFN alpha mRNAs. In L929 cells, only IFN beta, alpha 2, and alpha 4 genes were expressed efficiently following NDV induction and IFN alpha 9 mRNA was always below detectable level. Induction of macrophages with the synthetic inducer 10-carboxymethyl-9-acridanone resulted in small amounts of IFN alpha 2, alpha 4, and alpha 6 mRNAs and the IFN beta mRNA level was about 100-fold higher. Macrophages and L929 cells especially differed in the kinetics of IFN gene induction in that macrophages showed a much earlier transient expression of all IFN mRNA species. Additionally, IFN transcripts were degraded much faster in macrophage cultures than in L929cells. The IFN response of macrophages is thus characterized by a highly efficient control, providing a rapid onset and a rapid decline of IFN production, which limits release of IFN to a short time interval.

The non-specific stimulation of avian peripheral blood lymphocytes from uninfected chickens by paramyxoviruses and influenza viruses

Avian paramyxovirus-3 was mitogenic to peripheral blood lymphocytes (PBL) from about half the normal birds sampled from 3 inbred flocks. Eight other myxoviruses including Newcastle disease virus, Sendai virus and influenza virus were also irregularly mitogenic. This could complicate in vitro assays for specific immunity.

The synergistic neutralization of Newcastle disease virus by two monoclonal antibodies to its haemagglutinin-neuraminidase protein

Monoclonal antibodies (MAbs) to 2 epitopes on the haemagglutinin-neuraminidase (HN) protein of the Ulster strain of Newcastle disease virus neutralized synergistically: MAbs to HN-1 and HN-2 neutralized 1.2 and 1.7 log10 infectious units (i.u.) of virus when single as compared to 4.1 when combined. Although MAb to HN-1 but not to HN-2 inhibited haemagglutination they both neutralized more virus on desialyzed cells compared to normal cells and were considered to have interfered with viral attachments in a cooperative manner when combined. A third MAb to fusion (F) protein reduced infectivity by five log10 i.u. HN-1, HN-2 and F were not the only immunodominant epitopes because mutants, which simultaneously lacked all 3 epitopes, were indistinguishable from wild type when neutralized by polyclonal mouse, rabbit or chicken antiserum to whole virus.