LCos coronavirus son una granes are a large familia de patógenos bien y of well-establecidos deished pathogens of varios huéspedeus hosts, incluidos animales domésticos,ding domestic animales salvajes ys, wildlife, and humanos.
1. DOvescripción general delrview of SARS-CoV-2
LCo
s coronavirus
son una granes are a large famil
ia de patógenos bien y of well-establ
ecidos deished pathogens of vario
s huéspedeus hosts, inclu
idos animales domésticos,ding domestic animal
es salvajes ys, wildlife, and human
os s.[ 1 ] .
LosThe virus
que causaron brotes anteriores ees that caused previous outbreaks in human
os, caus
ando enfermedadesing severe respirator
ias graves, lesiones pulmonares y la muerte, son ely illness, lung injury, and death, are SARS-CoV (
coronavirus del síndromsevere acute respirator
io agudo severo) ey syndrome coronavirus) in 2003
y el and MERS-CoV (
coronavirus del síndromeMiddle East respirator
io de Oriente Medio) ey syndrome coronavirus) in 2012
[ 2 ] .
Un análisis genómico reciente con varias herramientasA recent genomic analysis with several bioinform
áticas demostró que elatics tools showed that SARS-CoV-2
tiene unhas a genom
a mue very similar
al delto the Bat coronavirus
Bat y el dominio de unión al and the receptor
binding domain (RBD)
de la gliof the spike glycoprote
ína espiga como elin like the Malayan pangolin coronavirus
. del pangolín malayo [ 3 ].
EThis
ta evidenc
iae indica
que el murciélago de herradura es etes that the horseshoe bat is the natural reservo
rio natural, y lair, and the main evidenc
ia principal sugiere que ele suggests that the Malayan pangol
ín malayo es un huésped in is an intermedia
riote host. [ 3 ] .
El SARS-CoV-2
es un virus envuelto con un ARN monocatenario de sentidois an enveloped virus with a single-stranded positiv
o. El tamaño dele-sense RNA. The genom
a de este patógeno varía de 29,8 kb a 29,9 kb e size of this pathogen ranges from 29.8 kb to 29.9 kb.[ 4 ] .
ElThe virus
codifica al menosencodes at least 29 prote
ínas. Las proteínas eins. The structural
es son proteínas de espiga proteins are spike (S), membran
ae (M), env
oltura (E) yelope (E), and nucleoc
ápsideapsid (NP)
proteins [ 5 ] .
Las proteínas no esNonstructural
e proteins (nsps)
tienen funcionehave functions neces
arias para la sary for replica
ción ytion and transcrip
ción en el ciclo de vida deltion in the viral life cycle virus [ 6 ] .
El tamaño de las partículas virales oscila entre 80 yViral particle size ranges from 80 to 120 nm
. [ 7 ] .
ElThe mec
anismo dehanism of viral infec
ción viral etion in human
os es a través de gotitas ys is through droplets and aerosol
es, que pueden viajar por el aires, which can travel through the air [ 8 ] .
La infección ocurre en células que expresanInfection occurs in cells expressing ACE2 (
enzima angiotensin-converti
dora de angiotensina 2) yng enzyme 2) and TMPRSS2 (
proteasa dtransmembrane serin
a transmembranae protease 2)
[ 9 ] .
La proteína S del coCoronavirus
se une aS protein binds to ACE2,
el principal receptor del the main SARS-CoV-2
que media la entrada del virus en las células, yreceptor that mediates viral entry into cells, and TMPRSS2
escinde lacleaves the S prote
ína S (en lasin (at the S1 and S2 subuni
dades S1 y S2) delts) of SARS-CoV-2,
lo que which facilita
la fusión deltes the fusion of SARS-
CoV-2
yand the cell membran
a celulare [ 9 ] [ 10 ] [ 11 ].
AIn add
emás, se ha demostrado que las cisteínaition, it has been shown that the cysteine proteas
as catepsina B y catepsina L es cathepsin B and endosomal
también puedencathepsin L may also contribu
ir a estete to this proce
soss. [ 10 ] [ 12 ] [ 13 ] .
En el tractoIn the respirator
ioy tract, ACE2
yand TMPRSS2
sare expres
an en las células ssed in the secretor
as y ciliadas de la nariz, las células sy and hair cells of the nose, the secretor
as y ciliadas de las vías respiratoriasy and hair cells of the conduct
oras, en las célulasing airways, in type II alveolar
es de tipo II en los pulmones y en la cells in the lungs, and in the corneal conjun
tiva corneal delctiva of the eye ojo [ 14 ] [ 15 ] [ 16 ] [ 17 ] .
The etiological virus of the pandemic has continuously evolved, with many variants emerging worldwide. Variants are categorized as the variant of interest, variant of concern, and variant under monitoring
[18]. There are five SARS-CoV-2 lineages designated as the variant of concern alpha, beta, gamma, delta, and omicron variants
[19]. These variants increase transmissibility compared to the original virus and potentially increase disease severity
[20].
2. Immune Response against SARS-CoV-2 in Brief
The SARS-CoV-2 infection involves diverse stages in the individual: start of infection, disease development, recovery, or systemic compromise. Each infection stage triggers and modulates innate and adaptative immune system mechanisms. Although SARS-CoV-2 is a virus that humanity is learning about, the immune response is equipped with mechanisms capable of dealing with this new threat. In the initial phase of SARS-CoV-2 infection, the individual presents a presymptomatic phase lasting up to 5 days, in which a high viral load is present
[21]. In these early days of infection, antibodies may not have been produced. Therefore, innate immunity is the first activated. The innate immune response comprises soluble and cellular components that respond nonspecifically against the virus. The cellular compounds include dendritic cells (DC), monocytes, macrophages, neutrophils, natural killer (NK) cells, and other innate lymphoid cells (ILCs)
[22]. Whereas soluble components include complement systems, soluble proteins, interferons, chemokines, and naturally occurring antibodies
[23]. Immune response cells recognize pathogen-associated molecular patterns (PAMPs) of SARS-CoV-2 through pattern recognition receptors (PRRs) such as Toll-like receptors (TLR), RIG-I-like receptors (RLR), and melanoma differentiation-associated protein 5 (MDA5). The viral sensing triggers the activation of signaling pathways which induce the production of immune mediators to generate an antiviral state mainly mediated by type I (IFN-α/β) and type III (IFN-λ) interferons (IFNs)
[24]. Reports have described that robust IFNs production during the early stage of infection is required to have a protective innate immune response against the virus
[25]. On the contrary, an inadequate and slow response to type I and type III IFNs due to virus evasion mechanisms, host comorbidities, or genetic defects cause an exacerbated immune response. This inadequate response induces elevated levels of chemokines (CCL2, CCL8, CXCL2, CXCL8, CXCL9, and CXCL16), high expression of proinflammatory cytokines such as IL-6, IL-10, IL-1, and TNF, in addition to activation, and recruitment of immune cells
[26][27]. The called “cytokine storm” leads to unbalanced levels of proinflammatory and antiviral mediators that remain the leading cause of ARDS and multi-organ failure
[25][26][28].
On the other hand, the adaptive immune response is orchestrated by CD8+ T lymphocytes, TCD4+, and B lymphocytes, responsible for immunological memory. In response to SARS-CoV-2 infection, it has been shown that non-severe patients or patients with mild symptoms have a low viral load and may not have produced antibodies
[29][30]. In contrast, antibodies have been detected by immunoassay tests and biosensors in patients with severe symptoms or cases
[29][31]. Patients with a high viral load activate the humoral immune response in the first two weeks of infection
[32]. The first seroconversion of antibodies is against protein N, followed by protein S of SARS-CoV-2 in patients with disease symptoms
[33]. Immunoglobulins IgA and IgM begin to be detected within the first ten days of infection; however, both antibodies can cross-react with protein N, which is highly conserved among coronaviruses
[34][35]. Moreover, high levels of IgG1 and IgG3 are expressed ten to fourteen days after infection in patients with disease symptoms
[36][37]. Older adults and seriously ill individuals reach high specificity antibodies concentrations against SARS-CoV-2 S protein.
Due to the urgency of reducing thousands of people’s cases and deaths, scientists have developed several vaccines against COVID-19. Efforts are being made to apply vaccines with emergency use authorization to the world population. Vaccination elicits immune responses capable of potently neutralizing SARS-CoV-2. However, the available data show that most approved COVID-19 vaccines protect against severe disease but do not prevent the clinical manifestation of COVID-19
[38]. Instead, it has been demonstrated that new variants with mutations in the spike, the main target of neutralizing antibodies, can escape the neutralization of humoral immunity
[39][40].
3. SARS-CoV-2 Detection
Molecular tests or biosensors are the tools for detecting SARS-CoV-2 nucleic acids/ antigens/antibodies against the virus (
Figure 1). In the early part of the illness, viral particles and their subunits can be detected; beyond the first two weeks of illness onset, antibodies against the virus could be detected
[41]. The SARS-CoV-2 infection stage is highly correlated to the diagnostic technique recommended for the pandemic. Early diagnosis of the disease and isolation of infected people is key to controlling the transmission of SARS-CoV-2
[42][43]. In the initial phase of SARS-CoV-2 infection, the individual presents a presymptomatic phase lasting up to 5 days, in which a high viral load is present
[21]. During these early days of infection, antibodies may not be detected. Therefore, since the pandemic began, the diagnostic method has been based on detecting viral genes using the molecular PCR technique, the gold standard worldwide
[44][45][46]. The pandemic has exceeded the ability to identify the virus in laboratories using molecular techniques; this has motivated the development of new technologies for the rapid detection of SARS-CoV-2 that are easy to perform compared to molecular tests in clinical laboratories. LFIA has been the unique device approved and available to use in mass worldwide. Biosensors with transducers are developing in SARS-CoV-2 diagnostic. However, most nanomaterials used in these biosensors present interferences with contaminants in human samples compared to performance under experimental conditions. It is important to emphasize that LFIAs have the unique properties of availability, accessibility, economy, and POC (including home use), these characteristics that are not shared by all biosensors with a transducer. In addition, biosensors with transducers require exclusive handling in laboratories certified under the Clinical Laboratory Improvement Amendments of 1998
[47][48]. The FDA have to date approved only one piezoelectric biosensor
[47] (
Figure 1).
Figure 1. Principio de la prueba LFIA. La prueba LFIA detecta la molécula objetivo en una membrana absorbente con anticuerpos alineados para formar las líneas de prueba y control. La muestra se coloca en una almohadilla de muestra, luego migra a la almohadilla de conjugado, que contiene el conjugado inmovilizado, generalmente hecho de nanopartículas (oro coloidal, látex coloreado o fluorescente, celulosa coloreada) conjugadas con anticuerpos o antígenos. La muestra interactúa con el conjugado y ambos migran a la siguiente sección de la tira, donde se inmovilizan los componentes biológicos del ensayo (proteínas/anticuerpos/antígenos). En esta sección, se capturan el analito y el conjugado. El exceso de reactivo pasa a través de las líneas de captura y se acumula en la almohadilla absorbente. Los resultados se interpretan en la membrana de nitrocelulosa como la presencia o ausencia de las líneas de prueba y control.