The data
More than 1 million sexually transmitted diseases (also known as Sexually Transmitted Infections) are acquired every day worldwide [8].
STDs are passed from one person to another, mostly through sexual activity including vaginal, oral, and anal sex. It is possible to have an infection and not know it because of the lack of symptoms or mild symptoms [6].
Furthermore, even after the immediate impact of the infection, in most cases, these type of diseases have serious reproductive health consequences such as infertility, mother-to-child transmission, as well as stillbirth, neonatal death, low-birth-weight and prematurity, sepsis, pneumonia, neonatal conjunctivitis, congenital deformities, and even cancer. [8].
According to the World Health Organization, there are more than 30 different bacteria, viruses and parasites that are known to be transmitted through sexual contact. From these, HIV is listed as one with the greatest incidence, as well as a disese that remains uncurable to the moment.
UNAIDS shows us that 38.0 million people globally were living with HIV in 2019, of which 690,000 died.
The science
First of all, STIS can be classified according to their causative organism (bacterial, viral or parasitic), by clinical presentation (ulcers in genital, anal, oral and perianal tissues, urethral and vaginal discharge, or genital warts), by the different mechanisms through which they cause infections and evade immunity (like inflammatory response that can lead to pathology throughout the genital tract, including pelvic inflammatory disease, ectopic pregnancy and infertility, and degradation of the epithelium) [9].
Mucosal epithelial cells are the first barrier against infection, equipped with receptors, they initiate and modulate the inflammatory cascade aimed at inducing pathogen clearance [10]. Tight regulation of inflammation is required in order to avoid selfâdamage. In the case of STIs, a combination of immune evasion, potent induction of inflammation and poor natural immunity represents scenarios in which HIV entry may be increased.
TLRs signalling pathway
Further, Tollâlike receptors (TLRs) play an important role in detecting pathogens including STIs, and initiating innate and adaptive immune responses. TLRs bind to their cognate ligands, resulting in a signalling cascade that culminates in the expression of proâinflammatory cytokines. TLRs can be classified as both intracellular and extracellular, depending on their expression and where ligand recognition typically occurs [11].
TLRs recognize pathogenâassociated molecular patterns (PAMPs), including bacterial DNA, viral nucleic acid and viral proteins, with the eventual goal of inducing specific Tâcell and antibody responses.
Intracellular TLRs mainly detect viral infections. In contrast to many extracellular TLRs, which tend to recognize protein structures, intracellular expression of TLR3, TLR7, TLR8 and TLR9 mediates viral nucleic acid sensing [9].
Regarding other prevention mechanisms against STIs in women, its is known that the vaginal microbiome could also play a big role. Women with certain Lactobacillusâdominant communities are able to produce lactic acid and maintain a low mucosal pH, which inhibits the growth of pathogenic bacteria including STIs [9]. Epithelial cells of the genital mucosa produce glycogen, which allows Lactobacillus to flourish.
TLRs signal through the recruitment of specific adaptor molecules, leading to activation of the transcription factors NF-ÎșB and IRFs, which dictate the outcome of innate immune responses.
As of the anatomy of the vagina, we know that it has a cornified squamous epithelium of 28 cell layers, throughout the menstrual cycle. These cells are shed each day, thereby reducing the ability of pathogens to reach target cells deeper in the epithelium. Disruptions in this protective stratum corneum barrier are likely to increase transmission of many types of infections [13].
Worth-mentioning, women are in more risk during the periods previous to puberty and after menopause. With the absence of estrogen, the vaginal epithelium is thin and without glycogen, vaginal pH is near neutral, the microbiota is sparse, there is little lubrication, and sexual intercourse is very likely to cause trauma. All these factors are likely to increase transmission by both cell-free and cell-associated HIV [13].
Talking about risks, it is well-known that by having another STI, your probabilities of contracting HIV also increase. The reason for this is that conditions such as Bacterial Vaginosis (BV) promote the growth of types of bacteria that cuase an inflammatoryresponse. In other words, inflammation is a factor that increases the risk of getting HIV.
Human Immunodeficient Virus (HIV)
HIV is one of the worldâs most serious public health challenges. There were approximately 38 million people worldwide with HIV/AIDS in 2019. From those, about 7.1 million people still need access to HIV testing services.