Immunological imprinting shapes the specificity of human antibody responses against SARS-CoV-2 variants

The spike glycoprotein of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) continues to accumulate substitutions, leading to breakthrough infections of vaccinated individuals. It remains unclear if exposures to antigenically distant SARS-CoV-2 variants can overcome memory B cell biases established by initial SARS-CoV-2 encounters. We determined the specificity and functionality of antibody and B cell responses following exposure to BA.5 and XBB variants in individuals who received ancestral SARS-CoV-2 mRNA vaccines. BA.5 exposures elicited antibody responses that targeted epitopes conserved between the BA.5 and ancestral spike. XBB exposures also elicited antibody responses that primarily targeted epitopes conserved between the XBB.1.5 and ancestral spike. However, unlike BA.5, a single XBB exposure elicited low frequencies of XBB.1.5-specific antibodies and B cells in some individuals. Pre-existing cross-reactive B cells and antibodies were correlated with stronger overall responses to XBB but weaker XBB-specific responses, suggesting that baseline immunity influences the activation of variant-specific SARS-CoV-2 responses.

Immunological imprinting shapes the specificity of human antibody responses against SARS-CoV-2 variants

The spike glycoprotein of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) continues to accumulate substitutions, leading to breakthrough infections of vaccinated individuals and prompting the development of updated booster vaccines. Here, we determined the specificity and functionality of antibody and B cell responses following exposure to BA.5 and XBB variants in individuals who received ancestral SARS-CoV-2 mRNA vaccines. BA.5 exposures elicited antibody responses that primarily targeted epitopes conserved between the BA.5 and ancestral spike, with poor reactivity to the XBB.1.5 variant. XBB exposures also elicited antibody responses that targeted epitopes conserved between the XBB.1.5 and ancestral spike. However, unlike BA.5, a single XBB exposure elicited low levels of XBB.1.5-specific antibodies and B cells in some individuals. Pre-existing cross-reactive B cells and antibodies were correlated with stronger overall responses to XBB but weaker XBB-specific responses, suggesting that baseline immunity influences the activation of variant-specific SARS-CoV-2 responses.

Evidence against the involvement of Mycobacterium ulcerans in most cases of necrotic arachnidism

Cutaneous lesions caused by M. ulcerans were shown to bear only a superficial resemblance to those produced by certain spider species. M. ulcerans was not found in either the venoms or the midguts of several Australian spiders, and deliberate contamination by inoculation of the fangs and digestive system of the wolf spider, Lycosa godeffroyi, did not result in permanent colonization. M. ulcerans was successfully introduced into the skin of mice through a small trauma site similar to that caused by a spider bite. However, because M. ulcerans was shown to survive on exposed surfaces for only a short period, a successful inoculation is likely only if the skin is contaminated with this organism after, or at the same time as, the skin suffers damage. The claim by other workers that M. ulcerans produces cutaneous ulcers by release of an exotoxin could not be confirmed. The authors conclude that M. ulcerans is not involved in most cases of necrotic arachnidism and hence there is no justification for prescribing anti-mycobacterial antibiotics to resolve alleged spider bite lesions unless the presence of M. ulcerans has been demonstrated by appropriate laboratory tests.

A comparison of the toxicity of the venoms of twelve common Australian spider species on rodent vital organ systems

1. Venom samples from twelve different Australian spider species were compared for their toxic effects on the heart and respiratory systems of anaesthetized rats. 2. The first and most serious effect of all venoms was on breathing, cardiotoxicity mostly being secondary to respiratory failure. 3. Only Atrax infensus and Selenocosmia stirlingi venoms proved highly toxic to rats, and therefore potentially toxic to humans, when single doses were used. 4. The low potency of most of the other venoms tested showed that several simultaneous spider bites would be necessary to cause significant toxicity.

The involvement of collagenase in the necrosis induced by the bites of some spiders

1. The midgut extracts of 13 Australian spider species produced cellular disruption in mouse skin in tissue culture conditions. 2. Microbial collagenase and the venoms of some of these species had similar effects. 3. Five venoms also caused severe dermonecrosis in living mice. 4. Pre-mixing the venoms with L-cysteine caused complete in vivo and partial in vitro inhibition of their effects. 5. It was concluded that collagenase is a major factor in the aetiology of necrotic arachnidism.

Studies of the necrotic actions of the venoms of several Australian spiders

1. Raw venoms from a number of Australian Araneomorph spiders were found to cause epidermal disruption in cultured skin from both mice and humans. 2. The more potent ones also caused loss of epidermal cell-cell adhesion of mouse skin in vivo. 3. Raw venoms from three Mygalomorph species did not have these actions. 4. Venom gland extracts from the Araneomorph species were also ineffective. 5. It was concluded that where spider venoms appear to possess necrogenic activity the most likely reason for this is contamination of the venoms with digestive tract secretions.

Some studies of the oedematogenic action of the venom of funnel-web spiders (Atrax species)

The ability of the venoms of Atrax infensus and two other funnel-web spider species to induce oedema in rats was investigated and it was found that all Atrax venoms tested caused strong Evans blue leakage from adjacent blood vessels when injected subcutaneously. This dye leakage did not diminish significantly either when the neurotoxin in the venom was first neutralized by pre-mixing with a rat serum protein preparation or when the sensory nerves supplying an area of skin were severed 4 days prior to its envenomation. The pattern and speed of Evans blue extravasation caused by female A. infensus venom resembled that for histamine and for 5-hydroxytryptamine, and pretreatment with an antihistamine-antiserotonin mixture caused essentially complete blockade of the oedematogenic action of this venom, although neither inhibitory drug was very effective when used individually. It was concluded that this venom induces local oedema in rats mainly by causing mast cell degranulation. In confirmation of this, the mast cells in the rat skull periosteal membranes were found to be extensively degranulated by exposure to the venom. Surprisingly, whole-rat envenomation, using very large doses of venom, produced little dye leakage even though obvious symptoms of neurotoxic action were observed.

The effects of season of collection, feeding, maturation and gender on the potency of funnel-web spider (Atrax infensus) venom

Assays of the venom of adult male and female as well as immature funnel-web spiders (Atrax infensus) were performed both at the end of the winter hibernation period and during the active summer months. For both sexes an increase in venom potency appeared to have occurred with the approach of summer, the venom of adult males then being clearly more potent than that of adult females. However, it was also found that, at least for adult females, forced abstinence from feeding was associated with an increase in venom potency, while feeding (at least on one insect species that A. infensus is known to accept as prey) seemed to lead to a lowered potency. From these observations it was concluded that the neurotoxin in the venom of female (and presumably also male) A. infensus spiders is probably synthesized in the venom glands rather than being extracted from the prey on which A. infensus normally feeds.

The chemical nature of the funnel-web spider venom inhibitor found in rat plasma

Strong evidence has been obtained that the funnel-web spider venom inhibitor, previously found to occur naturally in the blood of rats, is at least partly immunoglobulin in composition. However, the results of chromatographic and immunological studies, including the use of specific antisera, indicate that this inhibitor is not a single chemical entity and apparently resides within more than one immunoglobulin class. In addition, it was observed that challenge of rats with Atrax venom substantially increased the venom-inhibiting powers of their blood and that these powers were located in the same plasma fractions as in unchallenged rats.

Comparisons of the neurotoxic activity of the venom of several species of funnel web spiders (Atrax)

A bioassay has been developed to allow comparison of the neurotoxic activity of the venom of individuals of the four most common species of funnel web spiders (Atrax species). In the absence of purified Atrax neurotoxin, the stimulatory action of the venom on skeletal muscle from the cane toad, Bufo marinus, was compared with that of known concentrations of acetylcholine. Several experiments to validate the assay were performed, then venom samples from both male and female spiders were assayed. It was found that individual female spiders of all Atrax species normally secreted several times as much venom as male spiders, but its neurotoxicity was extremely variable and generally much lower. Both sexes tended to secrete more potent venom in summer than in other seasons. Both also showed some decrease in venom volumes and potencies if repeatedly milked at short intervals. All four Atrax species were found to have approximately equal levels of neurotoxic activity.

Naturally occurring inhibitors of the venom of funnel web spiders (Atrax species)

It has been shown that the blood plasma of rats and many other vertebrate species, but not man, contains a factor that inhibits the toxic actions of the venom of funnel web spiders (Atrax) on isolated toad voluntary muscle and rat lung preparations and also on anaesthetized whole rats. This factor was found to be effective against all obvious symptoms produced by the venom of both sexes of A. infensus and of the females of the other three common species of Atrax, particularly when administration of the factor to the test preparation preceded that of the venom.

Funnelweb-spider venom antagonist

It was found in a series of experiments on anaesthetized monkeys that rat plasma and rat euglobulin fractions contain a substance which could offer some protection against funnelweb-spider envenomation when administered before envenomation or simultaneously with the funnelweb-spider venom. Further work to isolate, identify, and purify this substance is needed.