The Effect of Testosterone on Vaccine Administration in the Immune System at a Molecular and Macroscopic Level

Introduction

Vaccination has long been recognized as one of the most effective preventive measures

against infectious disease. Vaccines target and stimulate the immune system to trigger a response

and provide antibodies against potentially dangerous infectious disease. This stimulation allows

the immune system to recognize and remove pathogens, thereby reducing morbidity and

mortality rates. As the process of developing and administering vaccines evolve, there is a

growing awareness of the consideration of who the recipients are of the vaccines. For example,

there has been more attention drawn to the biological sex of the recipients of vaccines.

New research into this topic has revealed that the biological sex of the person receiving

the vaccine has an impact on how they respond to it. Males and females have different levels of

hormone levels such as testosterone that affect their biological processes. This blatant difference

can induce different responses to vaccine administration. This newfound data has raised some

questions regarding the current “one size fits all” approach to vaccine administration.

The objective of this literature review is to analyze the role of testosterone levels in

vaccine responses among biological humans and to evaluate the possible need for personalizing

vaccines based on sex. By analyzing the existing scholarly research, this review will address the

pressing question: "What is the effect of testosterone levels on vaccine administration in humans:

Should personalized vaccines be introduced based on sex?

Search Methods

To obtain a sufficient review of the scholarly literature on the topic of hormone effects in the

immune system and its relation to vaccines, numerous databases were used. These included

scholarly information domains such as EBSCO, Google Scholar, and the University of South

Florida Library. The terms searched in databases that refined the research were as such: Immune

System, Cytokines, Lymph nodes, T-Cells, Testosterone in Immune system, Vaccines in Immune

system. The literature was restricted to sources presented between 1990 and Present (2024).

The Immune Response

The immune system is a vital part of the human body for overall health. An immune response is

triggered when a vaccine is introduced to the body. This immune response can be affected by a

multitude of factors, including age, preexisting medical conditions, and even sex. When a

vaccine is given, there is often early inflammatory events that follow (Siegrist 2016). The

immune system uses two different types of responses to combat invading pathogens. One

response is Innate, which occur to the same extent no matter how many times the infectious

agent interferes with the body (Delves 2000). The other response is the adaptive or acquired

response, which improves the responses as the immune system encounters the given infection

repeatedly (Delves 2000)

The immune system uses Innate and acquired responses which often work together to eliminate

pathogens (Delves 2000). In the adaptive (also referred to as acquired) response, the body

acquires new types of immune cells to fight pathogens, known as B and T lymphocytes, often

called B and T cells (Yatim 2015). The initial detection of pathogenic agents is typically done by

the innate immune system; although, B-cells may also complete this task (Clem 2011).

Specifically, the immune system detects epitopes on antigens, which are small subregions on the

antigens that trigger recognition, and consequently an immune response. The Innate response

will use antigen-presenting cells such as macrophages or monocytes to attach and bind to the

infectious agents (Clem 2011). The macrophages or monocytes will then insert the processed

antigen along with the MHC protein onto the surface of the antigen-presenting cell (Clem 2011).

The way that the vaccine induces immunity can be even further delved into. The response

to a bacterial infection is different than one of a viral infection. The viral antigen will be

connected to the MHC I protein and presented by the antigen-presenting cell to a CD8 cell which

will likely trigger cell-mediated immunity. On the other hand, if it is a bacterial or parasitic

antigen, the antigen will be bound with MHC II protein and presented by the antigen-presenting

cell to a CD4 cell which will likely trigger antibody-mediated immunity (Clem 2011).

In the immune system, white blood cells play an important role in its immune function.

Lymphocytes and Monocytes are two types of white blood cells. Monocytes are a part of the

body’s first line of defense and are especially important in innate immunity and Lymphocytes are

specifically vital in the adaptive response of the immune system. Both types produce cytokines,

which aid in the (re)modeling of tissues, whether it is developmentally programmed,

constitutive, or unscheduled (Nathan 1991). As we delve into the molecular processes of the

immune system, it is important to know the types of cytokines that originate from these

Monocytes and Lymphocytes. Specifically, Lymphocytes produce IL-2 cytokines as well as

others. The T cells and clones allow production of IL-2, IFNr, and TNF8, or IL-4, IL-5, IL-6, IL-

lo, and IL-13 as their unique products (Paul 1994). These are interleukins and interferons that

coordinate immune responses. Monocytes release cytokines like tumor necrosis factor (TNF) and

interleukin-1 (IL-1).

Cell membranes also play an important role in the immune system. Arachidonic acid is a

crucial part of these cell membranes and has specific properties that can affect the immune

system. Arachidonic acid is a polysaturated fatty acid, its chemical formula is C20H32O2 20:4

(ω-6), which characterizes many of its properties. 20:4 refers to the 20-carbon atom chain along

with four double bonds (Hanna 2018). (ω-6) refers to “the position of the first double bond from

the last, omega carbon atom” (Hanna 2018).

Arachidonic acid has four double bonds in the cis position which allows interaction with

proteins and consequently providing fluidity, even at low temperatures (Hanna 2018).

Furthermore, the four double bonds also enable interaction with oxygen which leas to bioactive

oxygenated molecules through enzymatic and non-enzymatic mechanisms (Hanna 2018). When

arachidonic acid is released, it is metabolized by key enzymes and leads to the formation of

different eicosanoids. These include the Cyclooxygenase Pathway, which converts into

prostaglandins and thromboxanes; and the Lipoxygenase Pathway, which converts into

leukotrienes and lipoxins (Samuelsson 1987). Prostaglandins, thromboxanes, and leukotrienes all

play a role in promoting inflammation. This allows for an effective immune response by

allowing T and B cells to access and target pathogens or damaged tissues. Lipoxins, on the other

hand, help resolve inflammation, promoting a shift from an active immune response to tissue

healing and recovery.

Testosterone and the Immune System

It has long been known that testosterone is regarded as an immune suppressor.

Consequently, this brings credence to the hypothesis of vaccine administration being affected by

testosterone. The hormone testosterone can affect the cytokine production, so therefore, this can

induce a difference in the immune responses of people of the opposite sex. A study done in 2004

by Elske Posma, Henk Moes, Maas Jan Heineman, and Marijke M. Faas explores this. They

observed how there was a difference in specific cytokines production such as a decreased

percentage of interleukin (IL)-2-producing lymphocytes, increased percentage of IL-12, IL-1β,

and increased percentage of tumor necrosis factor (TNF)-α-producing monocytes in males

compared with females (Posma 2004). The researchers investigated whether testosterone is a key

player in this difference.

The results showed interesting findings that led to the team’s conclusion. The key results

were that a substantial decrease in the percentage of IL-2 cytokines producing lymphocytes after

stimulation of the male lymphocytes in comparison to the female lymphocytes. Nevertheless,

there was a difference in the percentage of IL-4 and IL-10 lymphocytes, as well as IFN- γ

producing lymphocytes in males and females. Furthermore, there was an increase in the

forementioned IL-12, IL-1β, and TNF-α cytokines producing monocytes in males rather than

females. This led the researchers to look at how testosterone played a role in this cytokines

production from both monocytes and lymphocytes. They found no effect of testosterone in the

production of IL-2 cytokines or the IFN-γ cytokines. Moreover, they found that testosterone does

play a significant role in the production of IL-12 and IL-1β by monocytes and increases the

number of cells producing the cytokines.

Testosterone and Vaccine Efficacy – Study Analysis

Wunderlich and colleagues

The effect of Testosterone on Vaccines is an interesting topic, especially due to

Testosterone being widely known as an immunosuppressive agent. A plethora of studies have

been reviewed with a relation to varying types of vaccines to showcase the best discussion of this

topic. Wunderlich; F. Thomas explains that testosterone was found to suppress the development

of protective immunity in mice against infections with malaria parasites (Wunderlich 1993).

Consequently, a study was done on mice to showcase the specific effects of testosterone

on the vaccine. The experiment used a s Plasmodium Chabaudi model, which assisted in

providing insight into the relationship between hormone levels and vaccine administration. The

mice experimented on in this study were from the inbred strain B 10.A and were given an anti-

disease vaccine which composed of surface membranes of P. chabaudi-infected erythrocytes

(Wunderlich 1993). The surface membranes are referred to as ghosts because they are infected

cells, rid of their internal components, but still retaining the infected “neo-proteins" (Wunderlich

1993). These ghosts acted as antigens to stimulate an immune response due to their infectious

properties. As mentioned previously, the vaccine is anti-disease, which targets the disease to

improve symptoms.

A group of the mice were selected, after the vaccine was administered, to receive periodic

doses of testosterone. The testosterone was administered subcutaneously, twice a week for four

weeks (Wunderlich 1993), which allowed for slower absorption into the bloodstream. The goal

was to observe if testosterone affects the immune system’s response to a vaccine and also the

“challenge” with infected erythrocytes (Winderlich 1993). This model clearly shows the effect of

testosterone at both a molecular and macroscopic level and examines how hormonal modulation

may affect the efficacy of the vaccine by suppressing the immune system.

Therefore, with the experiment being done with a control group and an experimental

group, the researchers assessed whether the mice with testosterone treatment showed a reduced

immune response compared to the untreated population. The studies findings showed that male

mice exhibited reduced survival rates and impaired vaccine-induced immunity compared to their

female counterparts. The experiment showed that only 55% of the mice population treated with

testosterone were converted to self-healers, but in fact, a substantial 84% of the female

population converted to self-healers. This indicated a difference in response due to sex,

specifically there was a difference is immune response modulation. The data gives credence to

the hypothesis that since testosterone suppresses the immune system, it impairs the efficacy of

vaccines by reducing the immune system’s ability to give a sufficient response.

The effect of testosterone treatment on vaccine efficacy is further proved in the dosage of

the hormone. There were multiple doses administered to the experimental group and each dosage

produced findings that overall coincided with the study’s conclusion. Even at the lowest dose of

30 micrograms (0.03 mg), there was a notable decline in survival rates compared to the control.

And then at the highest dose of 0.9 mg, the percentage of mice that converted to self-healers

dropped to 34%. Moreover, testosterone had long lasting experimental effects. The obvious

impairment lasted for weeks following the treatment’s end. Even 10 weeks after the testosterone

treatment was discontinued, only about 60% of the testosterone-treated mice could be converted

to self-healers, which differs from the 100% of control mice. This shows the level of suppression

of immune system functionality due to testosterone.

Furman and colleagues

Another comprehensive analysis done by David Furman and colleagues also provides

insight into the effects of testosterone on vaccines in the immune system. This study analyzes the

trivalent inactivated influenza vaccine (TIV) and testosterone's effect on it in the immune system.

The study used participants that were either male or female to analyze the neutralizing antibody

response to the TIV. The researchers investigated this using numerous immune system

components such as serum cytokines, chemokines, blood cell subset frequencies, genome wide

genome expressions, and different responses to vitro stimuli. The study was done on close to 100

total participants, with 53 females and 34 males (Furman 2014).

The study used baseline data from a previously published viable source where 91 healthy

donors, in 2008 and 2009, participated in an influenza vaccine study at the Stanford-Lucile

Packard Children’s Hospital Vaccine Program.This was the case apart from the neutralizing

antibody response to the vaccine and the “determination of testosterone measurements from the

serum” (Furman 2014). The participants were separated based on the measurement taken, these

separations were made based on age, sex, BMI range and more.

The blood was taken pre-vaccination and 21-35 days after the TIV administration. The

blood was used for gene expression analysis. The peripheral blood mononuclear cells were then

obtained through a process called density gradient centrifugation and kept at – 80 degrees

Celsius and transferred to liquid nitrogen for preservation. To process the serum, before use, the

serum was separated by centrifugation of clotted blood and stored at – 80 degrees. Peripheral

blood mononuclear cells, also called PBMCs, along with whole blood, and serum were used for a

variety of purposes, including levels of cytokines and chemokines, gene expression analysis,

leukocyte subset frequency, testosterone levels, and CMV and EBV serostatus (Furman 2014).

Samples of the serum from both day 0 and the last day were used for virus microneutralization

titer determination (Furman 2014).

The results of the study showed an inverse correlation between the antibody responses

and testosterone levels. As noted previously, testosterone is an immune suppressor, but the data

in this study that focuses on the antibodies, further refines and supports this generalization. The

study, using the contrast between men and women, found that women had a better and more

robust antibody response than the male counterparts. This could be attributed to the higher levels

of pro-inflammatory cytokines (Furman 2014). Moreover, this could be linked to the fact that

testosterone inhibits antibody responses. The study narrowed further to include molecular

mechanisms present in testosterone and vaccine efficacy. Furman and colleagues discussed the

pathway of arachidonic acid. arachidonic acid is a polysaturated fat that plays a pivotal role in

the inflammatory response and the immune response. When a vaccine is administered, cells are

stimulated and enzymes release arachidonic acid from cell membranes, but testosterone can

influence the expression of the genes in the arachidonic acid. Testosterone has been found to

shift these toward a more anti-inflammatory phenotype, which is shown by reduced production

of pro-inflammatory mediators. Furthermore, mechanisms have been found in the study, such as

testosterone being able to bind to androgen receptors in immune cells. This leads to the

upregulation or downregulation of genes involved in arachidonic acid metabolism. At a

macroscopic level, this provides relevant information to support the assumption that testosterone,

as an “immune suppressor”, can weaken the immune response to a vaccine administered in the

body (Furman 2014).

Discussion

By analyzing different arguments, assumptions, and conclusions in the scholarly

conversation surrounding how testosterone plays a role in a vaccine’s effect on the immune

system, common themes can be analyzed to effectively review the literature. Many studies

assumed and concluded that testosterone is an immune suppressor. With the given notion that

men have an unsatisfactory immune response in comparison to women, studies such as one done

by Furman and colleagues, one by Wunderlich and colleagues, along with a study by Elske

Posma and colleagues have concluded that this is highly correlated to vaccine efficacy.

Another common theme is the molecular mechanisms that underlie tesosterones

suppresion of the immune system. One key mechanism involves the influence of testosterone on

arachidonic acid metabolism. As discussed earlier, arachidonic acid is a polyunsaturated fatty

acid that plays a crucial role in inflammation and immune cell activation (Furman 2014).

Ultimately the expression of genes involved in arachidonic acid metabolism can be changed by

testosterone and effectively make the response to vaccines weaker.

The findings of these studies and scholarly journals have a significant impact on public

health. Understanding the impact of testosterone on the effects of vaccines can lead to further

research and academic discussion, which could then be applied to inform the development of

personalized vaccines or vaccination strategies based on sex. Moreover, this research can have a

profound impact on vaccination strategies for those with high testosterone levels and therefore

improve vaccine efficacy. Future research could provide insight into the molecular mechanisms

through experimental data collection and analysis. This could involve investigating the specific

genes and pathways involved in the regulation of the immune response by testosterone.

Additionally, studies could be done to experimentally determine if personalized vaccines are a

viable option to improve vaccine efficacy and improve public health.

Conclusion

In conclusion, the research presented shows how testosterone significantly affects

vaccine efficacy. With the conclusion that, because of testosterone's effect on the immune

system, men often have a weaker immune response to vaccines than women. The scholarly

conversation suggests that biological differences, particularly hormone levels, play a significant

role in vaccine response. The implications for personalized vaccine strategies based on sex

should be carefully considered, especially when aiming to optimize public health outcomes.

Future research should focus on developing and testing sex-specific vaccine protocols to ensure

equitable and effective protection for all recipients.

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