Dear Colleagues,

The immune system refers to a variety of cells and processes that have the crucial role of protecting the skin, respiratory, and intestinal tracts and other areas of our body from foreign antigens such as bacteria, fungi and viruses. The first line of defense is represented by the non-antigen-specific innate immune arm, which is exploited by the host immediately after encountering the microbial pathogen. Besides anatomical and physiological barriers, several innate immune cells are involved in this first defense, such as macrophages, dendritic cells, neutrophils, basophils, eosinophils, mast cells, natural killer cells and innate lymphoid cells. These cells exploit a vast array of pathogen-recognition receptors (PRRs) to detect common structures of several microbes known as pathogen-associated molecular patterns (PAMPs), such as bacterial lipopolysaccharides or double-stranded ribonucleic acid produced during viral infections. Microbial phagocytosis and killing by phagocytic cells as well as prompt cytokine and chemokine production at the site of infection are responsible for the first defense, inflammation and recruitment of immune cells. The complement system takes part in the innate immune response by targeting and opsonizing several microbial pathogens, thereby facilitating phagocytosis and killing.

The second line of defense is represented by the adaptive immune response, which specifically recognizes microbial antigens, eliminates infected cells and develops a long-term immunological memory. T lymphocytes after antigen presentation by professional antigen-presenting cells proliferate and exert their effector functions, and B lymphocytes differentiate into plasma cells to produce antibodies.

Females have both innate and acquired immunological responses stronger than males due to biological factors (i.e., genetic and epigenetic factors or sex hormones) and to psychosocial factors (i.e., gender differences). In particular, females show a more effective phagocytosis and antigen presentation, a stronger production of cytokines in response to infections, a higher absolute number of CD4 + T lymphocytes and higher levels of circulating antibodies in comparison to males. The increased activation of the immune response is a double-edged sword because it makes females more resistant to some infections but more susceptible to inflammatory and autoimmune diseases. Males and females of certain species, ranging from humans to horses and rodents, differ in their responses to and the outcomes of diverse pathogenic infections. In most cases, the precise mechanism mediating the dimorphism in infectious disease pathogenesis is not known, in part because sex has not been evaluated as a biological variable for the analysis of outcome data.

This Special Issue will explore new insights in the study of cellular mechanisms involved both in the innate and acquired immune response to bacteria, fungi, viruses and parasites, also taking into account sex differences in infectious disease pathogenesis.

Dr. Maria Cristina Gagliardi 
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. International Journal of Molecular Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. There is an Article Processing Charge (APC) for publication in this open access journal. For details about the APC please see here. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• innate immune cells
• inflammatory/antinflammatory cytokines
• antigen presenting cells
• complement
• antimicrobial T and B cell response
• sexual dymorphism